optimize png images losslessly using zopflipng

Resend https://github.com/gitlabhq/gitlabhq/pull/10354#issuecomment-222194091

Optimized 246 png images losslessly using Google's zopflipng.
```
 app/assets/images/auth_buttons/azure_64.png        | Bin 986 -> 695 bytes
 app/assets/images/auth_buttons/bitbucket_64.png    | Bin 2163 -> 2161 bytes
 app/assets/images/auth_buttons/facebook_64.png     | Bin 2970 -> 870 bytes
 app/assets/images/auth_buttons/github_64.png       | Bin 2625 -> 1151 bytes
 app/assets/images/auth_buttons/gitlab_64.png       | Bin 2849 -> 2070 bytes
 app/assets/images/auth_buttons/google_64.png       | Bin 5281 -> 4366 bytes
 app/assets/images/auth_buttons/twitter_64.png      | Bin 4835 -> 3110 bytes
 app/assets/images/bg_fallback.png                  | Bin 167 -> 167 bytes
 app/assets/images/dark-scheme-preview.png          | Bin 3996 -> 3992 bytes
 app/assets/images/emoji.png                        | Bin 263533 -> 263346 bytes
 app/assets/images/emoji@2x.png                     | Bin 690504 -> 689076 bytes
 app/assets/images/gitlab_logo.png                  | Bin 5189 -> 3616 bytes
 app/assets/images/gitorious-logo-black.png         | Bin 809 -> 631 bytes
 app/assets/images/gitorious-logo-blue.png          | Bin 495 -> 201 bytes
 app/assets/images/icon-link.png                    | Bin 1128 -> 729 bytes
 app/assets/images/images.png                       | Bin 5849 -> 5806 bytes
 app/assets/images/monokai-scheme-preview.png       | Bin 3711 -> 3708 bytes
 app/assets/images/msapplication-tile.png           | Bin 5798 -> 4328 bytes
 app/assets/images/no_avatar.png                    | Bin 621 -> 621 bytes
 app/assets/images/no_group_avatar.png              | Bin 942 -> 939 bytes
 app/assets/images/slider_handles.png               | Bin 1377 -> 1341 bytes
 app/assets/images/touch-icon-ipad-retina.png       | Bin 8130 -> 5662 bytes
 app/assets/images/touch-icon-ipad.png              | Bin 3493 -> 2465 bytes
 app/assets/images/touch-icon-iphone-retina.png     | Bin 4997 -> 3460 bytes
 app/assets/images/touch-icon-iphone.png            | Bin 2766 -> 1949 bytes
 doc/administration/img/housekeeping_settings.png   | Bin 23856 -> 19347 bytes
 .../img/build_artifacts_browser.png                | Bin 89132 -> 82102 bytes
 .../img/build_artifacts_browser_button.png         | Bin 11614 -> 7230 bytes
 doc/ci/img/builds_tab.png                          | Bin 3845 -> 3047 bytes
 doc/ci/img/features_settings.png                   | Bin 18691 -> 15809 bytes
 doc/ci/quick_start/img/build_log.png               | Bin 63272 -> 52482 bytes
 doc/ci/quick_start/img/builds_status.png           | Bin 49121 -> 41838 bytes
 doc/ci/quick_start/img/new_commit.png              | Bin 9033 -> 7587 bytes
 doc/ci/quick_start/img/runners_activated.png       | Bin 27597 -> 22822 bytes
 .../img/single_commit_status_pending.png           | Bin 36431 -> 29981 bytes
 doc/ci/quick_start/img/status_pending.png          | Bin 19782 -> 16205 bytes
 doc/ci/runners/project_specific.png                | Bin 31408 -> 30196 bytes
 doc/ci/runners/shared_runner.png                   | Bin 18366 -> 17797 bytes
 doc/ci/runners/shared_to_specific_admin.png        | Bin 5897 -> 5715 bytes
 doc/ci/triggers/img/builds_page.png                | Bin 39713 -> 33324 bytes
 doc/ci/triggers/img/trigger_single_build.png       | Bin 2895 -> 2387 bytes
 doc/ci/triggers/img/trigger_variables.png          | Bin 5418 -> 4433 bytes
 doc/ci/triggers/img/triggers_page.png              | Bin 15889 -> 12943 bytes
 doc/container_registry/img/container_registry.png  | Bin 354050 -> 222782 bytes
 doc/container_registry/img/project_feature.png     | Bin 392842 -> 248750 bytes
 .../branded_login_page/appearance.png              | Bin 365120 -> 156228 bytes
 .../branded_login_page/custom_sign_in.png          | Bin 314111 -> 166674 bytes
 .../branded_login_page/default_login_page.png      | Bin 292731 -> 150538 bytes
 doc/development/gitlab_architecture_diagram.png    | Bin 46947 -> 23831 bytes
 .../basicsimages/add_new_merge_request.png         | Bin 9467 -> 9003 bytes
 doc/gitlab-basics/basicsimages/add_sshkey.png      | Bin 1463 -> 1394 bytes
 doc/gitlab-basics/basicsimages/branch_info.png     | Bin 7978 -> 7572 bytes
 doc/gitlab-basics/basicsimages/branch_name.png     | Bin 2199 -> 2137 bytes
 doc/gitlab-basics/basicsimages/branches.png        | Bin 3653 -> 3548 bytes
 .../basicsimages/button-create-mr.png              | Bin 6154 -> 5927 bytes
 .../basicsimages/click-on-new-group.png            | Bin 2063 -> 1957 bytes
 doc/gitlab-basics/basicsimages/commit_changes.png  | Bin 5567 -> 4941 bytes
 doc/gitlab-basics/basicsimages/commit_message.png  | Bin 5707 -> 5103 bytes
 doc/gitlab-basics/basicsimages/commits.png         | Bin 4258 -> 4112 bytes
 .../basicsimages/compare_branches.png              | Bin 1624 -> 1520 bytes
 doc/gitlab-basics/basicsimages/create_file.png     | Bin 2524 -> 2451 bytes
 doc/gitlab-basics/basicsimages/create_group.png    | Bin 3224 -> 3184 bytes
 doc/gitlab-basics/basicsimages/edit_file.png       | Bin 2259 -> 2221 bytes
 doc/gitlab-basics/basicsimages/file_located.png    | Bin 3156 -> 3078 bytes
 doc/gitlab-basics/basicsimages/file_name.png       | Bin 2544 -> 2412 bytes
 doc/gitlab-basics/basicsimages/find_file.png       | Bin 8840 -> 8426 bytes
 doc/gitlab-basics/basicsimages/find_group.png      | Bin 6159 -> 5897 bytes
 doc/gitlab-basics/basicsimages/fork.png            | Bin 1046 -> 896 bytes
 doc/gitlab-basics/basicsimages/group_info.png      | Bin 16217 -> 15479 bytes
 doc/gitlab-basics/basicsimages/groups.png          | Bin 4857 -> 4752 bytes
 doc/gitlab-basics/basicsimages/https.png           | Bin 2887 -> 2822 bytes
 doc/gitlab-basics/basicsimages/image_file.png      | Bin 2939 -> 2796 bytes
 doc/gitlab-basics/basicsimages/issue_title.png     | Bin 9059 -> 8311 bytes
 doc/gitlab-basics/basicsimages/issues.png          | Bin 4332 -> 4153 bytes
 doc/gitlab-basics/basicsimages/key.png             | Bin 1264 -> 1177 bytes
 doc/gitlab-basics/basicsimages/merge_requests.png  | Bin 4381 -> 4213 bytes
 .../basicsimages/new_merge_request.png             | Bin 3227 -> 3162 bytes
 doc/gitlab-basics/basicsimages/new_project.png     | Bin 2319 -> 2234 bytes
 doc/gitlab-basics/basicsimages/newbranch.png       | Bin 1314 -> 1244 bytes
 doc/gitlab-basics/basicsimages/paste_sshkey.png    | Bin 8620 -> 7699 bytes
 .../basicsimages/profile_settings.png              | Bin 1194 -> 1101 bytes
 doc/gitlab-basics/basicsimages/project_info.png    | Bin 21862 -> 21041 bytes
 .../basicsimages/public_file_link.png              | Bin 3038 -> 3023 bytes
 doc/gitlab-basics/basicsimages/select-group.png    | Bin 6075 -> 6034 bytes
 doc/gitlab-basics/basicsimages/select-group2.png   | Bin 5049 -> 5040 bytes
 doc/gitlab-basics/basicsimages/select_branch.png   | Bin 12213 -> 11207 bytes
 doc/gitlab-basics/basicsimages/select_project.png  | Bin 16832 -> 16176 bytes
 doc/gitlab-basics/basicsimages/settings.png        | Bin 4321 -> 4149 bytes
 doc/gitlab-basics/basicsimages/shh_keys.png        | Bin 4981 -> 4782 bytes
 .../basicsimages/submit_new_issue.png              | Bin 9083 -> 8644 bytes
 .../basicsimages/title_description_mr.png          | Bin 12749 -> 11919 bytes
 doc/gitlab-basics/basicsimages/white_space.png     | Bin 3707 -> 2192 bytes
 doc/integration/img/akismet_settings.png           | Bin 55837 -> 26625 bytes
 .../img/enabled-oauth-sign-in-sources.png          | Bin 49081 -> 21767 bytes
 doc/integration/img/facebook_api_keys.png          | Bin 125921 -> 85832 bytes
 doc/integration/img/facebook_app_settings.png      | Bin 134387 -> 68086 bytes
 doc/integration/img/facebook_website_url.png       | Bin 42292 -> 19823 bytes
 doc/integration/img/github_app.png                 | Bin 75297 -> 55591 bytes
 doc/integration/img/gitlab_app.png                 | Bin 55325 -> 30963 bytes
 .../img/gmail_action_buttons_for_gitlab.png        | Bin 17321 -> 16020 bytes
 doc/integration/img/google_app.png                 | Bin 52669 -> 29154 bytes
 .../img/oauth_provider_admin_application.png       | Bin 40579 -> 33440 bytes
 .../img/oauth_provider_application_form.png        | Bin 27974 -> 23048 bytes
 .../img/oauth_provider_application_id_secret.png   | Bin 33901 -> 27673 bytes
 .../img/oauth_provider_authorized_application.png  | Bin 32225 -> 26622 bytes
 .../img/oauth_provider_user_wide_applications.png  | Bin 40632 -> 33337 bytes
 doc/integration/img/twitter_app_api_keys.png       | Bin 72200 -> 36921 bytes
 doc/integration/img/twitter_app_details.png        | Bin 121621 -> 64686 bytes
 doc/markdown/img/logo.png                          | Bin 11097 -> 9509 bytes
 doc/monitoring/img/health_check_token.png          | Bin 10884 -> 6630 bytes
 .../performance/img/grafana_dashboard_dropdown.png | Bin 29419 -> 14368 bytes
 .../performance/img/grafana_dashboard_import.png   | Bin 40974 -> 18267 bytes
 .../img/grafana_data_source_configuration.png      | Bin 53402 -> 26060 bytes
 .../performance/img/grafana_data_source_empty.png  | Bin 44058 -> 21821 bytes
 .../performance/img/grafana_save_icon.png          | Bin 16024 -> 9107 bytes
 .../img/metrics_gitlab_configuration_settings.png  | Bin 45148 -> 37228 bytes
 doc/profile/2fa.png                                | Bin 23415 -> 22047 bytes
 doc/profile/2fa_auth.png                           | Bin 15569 -> 14535 bytes
 doc/project_services/img/builds_emails_service.png | Bin 41222 -> 33943 bytes
 .../img/jira_add_gitlab_commit_message.png         | Bin 57136 -> 46590 bytes
 .../img/jira_add_user_to_group.png                 | Bin 59251 -> 41994 bytes
 doc/project_services/img/jira_create_new_group.png | Bin 41294 -> 32934 bytes
 .../img/jira_create_new_group_name.png             | Bin 12535 -> 9054 bytes
 doc/project_services/img/jira_create_new_user.png  | Bin 26532 -> 21081 bytes
 doc/project_services/img/jira_group_access.png     | Bin 46028 -> 32210 bytes
 doc/project_services/img/jira_issue_closed.png     | Bin 92601 -> 77028 bytes
 doc/project_services/img/jira_issue_reference.png  | Bin 39942 -> 36188 bytes
 doc/project_services/img/jira_issues_workflow.png  | Bin 105237 -> 87067 bytes
 .../img/jira_merge_request_close.png               | Bin 111150 -> 102835 bytes
 doc/project_services/img/jira_project_name.png     | Bin 60598 -> 41572 bytes
 ...jira_reference_commit_message_in_jira_issue.png | Bin 42452 -> 33706 bytes
 doc/project_services/img/jira_service.png          | Bin 59082 -> 56834 bytes
 .../img/jira_service_close_issue.png               | Bin 88433 -> 79569 bytes
 doc/project_services/img/jira_service_page.png     | Bin 49122 -> 36280 bytes
 .../img/jira_submit_gitlab_merge_request.png       | Bin 63063 -> 51913 bytes
 .../img/jira_user_management_link.png              | Bin 58211 -> 43095 bytes
 .../img/jira_workflow_screenshot.png               | Bin 121534 -> 111093 bytes
 doc/project_services/img/redmine_configuration.png | Bin 21061 -> 16973 bytes
 .../img/services_templates_redmine_example.png     | Bin 17351 -> 13936 bytes
 doc/raketasks/backup_hrz.png                       | Bin 21955 -> 8907 bytes
 doc/raketasks/check_repos_output.png               | Bin 73786 -> 35333 bytes
 .../img/two_factor_authentication_settings.png     | Bin 20399 -> 16807 bytes
 doc/web_hooks/ssl.png                              | Bin 77165 -> 39120 bytes
 .../img/add_new_user_to_project_settings.png       | Bin 22822 -> 18149 bytes
 .../add-user/img/add_user_email_accept.png         | Bin 22961 -> 22877 bytes
 doc/workflow/add-user/img/add_user_email_ready.png | Bin 40305 -> 40207 bytes
 .../add-user/img/add_user_email_search.png         | Bin 45884 -> 45798 bytes
 .../add-user/img/add_user_give_permissions.png     | Bin 56480 -> 56380 bytes
 ...dd_user_import_members_from_another_project.png | Bin 38874 -> 38778 bytes
 .../add-user/img/add_user_imported_members.png     | Bin 37873 -> 37835 bytes
 .../add-user/img/add_user_list_members.png         | Bin 24427 -> 24337 bytes
 .../add-user/img/add_user_members_menu.png         | Bin 42319 -> 42224 bytes
 .../add-user/img/add_user_search_people.png        | Bin 39941 -> 39844 bytes
 doc/workflow/award_emoji.png                       | Bin 16926 -> 9939 bytes
 doc/workflow/ci_mr.png                             | Bin 40065 -> 29571 bytes
 doc/workflow/close_issue_mr.png                    | Bin 146292 -> 82595 bytes
 doc/workflow/environment_branches.png              | Bin 40210 -> 20745 bytes
 doc/workflow/forking/branch_select.png             | Bin 55352 -> 27299 bytes
 doc/workflow/forking/merge_request.png             | Bin 60597 -> 31560 bytes
 doc/workflow/four_stages.png                       | Bin 20934 -> 10003 bytes
 doc/workflow/git_pull.png                          | Bin 167056 -> 94405 bytes
 doc/workflow/gitdashflow.png                       | Bin 184726 -> 131491 bytes
 doc/workflow/github_flow.png                       | Bin 20600 -> 10251 bytes
 doc/workflow/gitlab_flow.png                       | Bin 90883 -> 70871 bytes
 doc/workflow/good_commit.png                       | Bin 28433 -> 13131 bytes
 doc/workflow/groups/add_member_to_group.png        | Bin 138184 -> 78060 bytes
 doc/workflow/groups/group_dashboard.png            | Bin 107332 -> 59446 bytes
 doc/workflow/groups/group_with_two_projects.png    | Bin 129319 -> 73101 bytes
 doc/workflow/groups/max_access_level.png           | Bin 135354 -> 74947 bytes
 doc/workflow/groups/new_group_button.png           | Bin 185406 -> 108482 bytes
 doc/workflow/groups/new_group_form.png             | Bin 106491 -> 58860 bytes
 .../groups/other_group_sees_shared_project.png     | Bin 118382 -> 64447 bytes
 doc/workflow/groups/override_access_level.png      | Bin 157193 -> 90122 bytes
 doc/workflow/groups/project_members_via_group.png  | Bin 151339 -> 86260 bytes
 doc/workflow/groups/share_project_with_groups.png  | Bin 118868 -> 65633 bytes
 doc/workflow/groups/transfer_project.png           | Bin 164958 -> 92115 bytes
 doc/workflow/img/award_emoji_select.png            | Bin 65985 -> 49296 bytes
 .../img/award_emoji_votes_least_popular.png        | Bin 144501 -> 116715 bytes
 .../img/award_emoji_votes_most_popular.png         | Bin 136577 -> 108775 bytes
 .../img/award_emoji_votes_sort_options.png         | Bin 162251 -> 131659 bytes
 doc/workflow/img/cherry_pick_changes_commit.png    | Bin 353067 -> 304098 bytes
 .../img/cherry_pick_changes_commit_modal.png       | Bin 312659 -> 264883 bytes
 doc/workflow/img/cherry_pick_changes_mr.png        | Bin 252085 -> 212267 bytes
 doc/workflow/img/cherry_pick_changes_mr_modal.png  | Bin 225569 -> 186597 bytes
 doc/workflow/img/file_finder_find_button.png       | Bin 30974 -> 25458 bytes
 doc/workflow/img/file_finder_find_file.png         | Bin 42658 -> 35114 bytes
 .../img/forking_workflow_choose_namespace.png      | Bin 70405 -> 59114 bytes
 doc/workflow/img/forking_workflow_fork_button.png  | Bin 26438 -> 20750 bytes
 .../img/forking_workflow_path_taken_error.png      | Bin 22380 -> 17978 bytes
 doc/workflow/img/new_branch_from_issue.png         | Bin 120622 -> 54607 bytes
 doc/workflow/img/revert_changes_commit.png         | Bin 360098 -> 233750 bytes
 doc/workflow/img/revert_changes_commit_modal.png   | Bin 327932 -> 205046 bytes
 doc/workflow/img/revert_changes_mr.png             | Bin 367881 -> 241051 bytes
 doc/workflow/img/revert_changes_mr_modal.png       | Bin 335010 -> 211022 bytes
 doc/workflow/img/todos_icon.png                    | Bin 6320 -> 3843 bytes
 doc/workflow/img/todos_index.png                   | Bin 184839 -> 152040 bytes
 .../img/web_editor_new_branch_dropdown.png         | Bin 34233 -> 20436 bytes
 doc/workflow/img/web_editor_new_branch_page.png    | Bin 21618 -> 11245 bytes
 .../img/web_editor_new_directory_dialog.png        | Bin 26145 -> 13339 bytes
 .../img/web_editor_new_directory_dropdown.png      | Bin 33714 -> 20007 bytes
 doc/workflow/img/web_editor_new_file_dropdown.png  | Bin 34978 -> 20680 bytes
 doc/workflow/img/web_editor_new_file_editor.png    | Bin 128658 -> 66261 bytes
 doc/workflow/img/web_editor_new_push_widget.png    | Bin 11220 -> 7076 bytes
 doc/workflow/img/web_editor_new_tag_dropdown.png   | Bin 33753 -> 20080 bytes
 doc/workflow/img/web_editor_new_tag_page.png       | Bin 75536 -> 36610 bytes
 .../img/web_editor_start_new_merge_request.png     | Bin 14352 -> 8596 bytes
 doc/workflow/img/web_editor_upload_file_dialog.png | Bin 46219 -> 21502 bytes
 .../img/web_editor_upload_file_dropdown.png        | Bin 34835 -> 20651 bytes
 .../bitbucket_import_select_project.png            | Bin 16121 -> 15288 bytes
 .../fogbugz_importer/fogbugz_import_finished.png   | Bin 53276 -> 30266 bytes
 .../fogbugz_importer/fogbugz_import_login.png      | Bin 44444 -> 20797 bytes
 .../fogbugz_import_select_fogbogz.png              | Bin 35415 -> 20526 bytes
 .../fogbugz_import_select_project.png              | Bin 62552 -> 34836 bytes
 .../fogbugz_importer/fogbugz_import_user_map.png   | Bin 157856 -> 77208 bytes
 .../importing/gitlab_importer/importer.png         | Bin 40778 -> 18366 bytes
 .../importing/gitlab_importer/new_project_page.png | Bin 72663 -> 33589 bytes
 .../img/import_projects_from_github_importer.png   | Bin 28033 -> 22711 bytes
 ...mport_projects_from_github_new_project_page.png | Bin 17225 -> 13668 bytes
 doc/workflow/merge_commits.png                     | Bin 41422 -> 22181 bytes
 doc/workflow/merge_request.png                     | Bin 169503 -> 98070 bytes
 doc/workflow/merge_requests/commit_compare.png     | Bin 110376 -> 65010 bytes
 doc/workflow/merge_requests/merge_request_diff.png | Bin 166226 -> 103239 bytes
 .../merge_request_diff_without_whitespace.png      | Bin 121476 -> 71896 bytes
 doc/workflow/merge_when_build_succeeds/enable.png  | Bin 151112 -> 68769 bytes
 doc/workflow/merge_when_build_succeeds/status.png  | Bin 180318 -> 82655 bytes
 doc/workflow/messy_flow.png                        | Bin 33829 -> 19314 bytes
 doc/workflow/milestones/form.png                   | Bin 88591 -> 84872 bytes
 doc/workflow/milestones/group_form.png             | Bin 77087 -> 74429 bytes
 doc/workflow/mr_inline_comments.png                | Bin 193311 -> 117313 bytes
 doc/workflow/notifications/settings.png            | Bin 90986 -> 59256 bytes
 doc/workflow/production_branch.png                 | Bin 21716 -> 10946 bytes
 .../protected_branches/protected_branches1.png     | Bin 170113 -> 155815 bytes
 .../protected_branches/protected_branches2.png     | Bin 25851 -> 23208 bytes
 doc/workflow/rebase.png                            | Bin 123041 -> 68976 bytes
 doc/workflow/release_branches.png                  | Bin 44173 -> 22163 bytes
 doc/workflow/releases/new_tag.png                  | Bin 154755 -> 87330 bytes
 doc/workflow/releases/tags.png                     | Bin 165449 -> 93016 bytes
 doc/workflow/remove_checkbox.png                   | Bin 22272 -> 12339 bytes
 doc/workflow/share_with_group.png                  | Bin 53784 -> 50450 bytes
 doc/workflow/shortcuts.png                         | Bin 108255 -> 108209 bytes
 .../wip_merge_requests/blocked_accept_button.png   | Bin 65231 -> 32720 bytes
 doc/workflow/wip_merge_requests/mark_as_wip.png    | Bin 41549 -> 21640 bytes
 doc/workflow/wip_merge_requests/unmark_as_wip.png  | Bin 32151 -> 16606 bytes
 public/apple-touch-icon-precomposed.png            | Bin 11097 -> 9509 bytes
 public/apple-touch-icon.png                        | Bin 11097 -> 9509 bytes
 spec/fixtures/dk.png                               | Bin 1143 -> 1062 bytes
```

cc @connorshea

See merge request !4325