Fix issue description syntax highlighting and math rendering

Closes #33877

See merge request !12282

Update rainbow from 2.1.0 to 2.2.2.

See merge request !12289

Update paranoia from 2.2 to 2.3.1.

See merge request !12288

Remove implicit dependency on `gitlab_sign_in` assigning to a user instance variable

See merge request !12296

Update carrierwave from 1.0.0 to 1.1.0.

See merge request !12291

We shouldn't be using instance variables in specs to begin with, and
depending on this implicit behavior of `gitlab_sign_in` would have made
it more difficult to change to `sign_in` where possible.

...we've also gone ahead and changed to `sign_in` where possible.

Prepare for bypassing GitLab sign in in feature specs

See merge request !11913

Not sure why this fails with the full login flow, but it's not necessary
and would've been changed eventually anyway, so whatever!

Change `logout_direct` uses to `gitlab_sign_out_direct`

Change single `login_via` use to `gitlab_sign_in_via`

Restored missing function inside dropzone_input.js

Closes #33836

See merge request !12279

Enable autocomplete on project snippets

Closes #33911

See merge request !12286

- [x] Rename `login_as` to `gitlab_sign_in`
- [x] Rename `login_with` to `gitlab_sign_in_with`
- [x] Rename `login_via` to `gitlab_sign_in_via`
- [x] Rename `logout` to `gitlab_sign_out`
- [x] Rename `logout_direct` to `gitlab_sign_out_direct`
- [x] Make `gitlab_login_with` (née `login_with`) private
- [x] Make `mock_auth_hash` private

Changelog: https://github.com/carrierwaveuploader/carrierwave/blob/f2f8569b1013f601fe7be4b3a616359acd27240d/CHANGELOG.md#110---2017-04-30

Adds support for Rails 5.1

Changelog: https://github.com/sickill/rainbow/blob/master/Changelog.md#222-2017-04-21

Adds support for Ruby 2.4.

https://github.com/rubysherpas/paranoia/blob/core/CHANGELOG.md#230-2017-04-14

Adds support for Rails 5.1.

Adjust position and wording for related issues in merge requests

Closes #33652

See merge request !11759

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1210 disabled
autocomplete for personal snippets and project snippets. But we want
autocomplete on project snippets.

Re-enable autocomplete for milestones, tags, releases, and wiki

Closes #33598

See merge request !12110

Disable autocomplete on snippets comments

Closes #33594

See merge request !12108

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/33877

Regressed in
https://gitlab.com/gitlab-org/gitlab-ce/commit/5a95d6f8dae00b31b694759c6ddbf6d83b1a7890#3a15290e7696397415523e0b664aceb3dd4010ae_0_46
where the ref no longer matches what we call `renderGFM` on.

If migrations are pending, make CurrentSettings use existing values and populate missing columns with defaults

See merge request !12253

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/33594

Was supposedly fixed in MR for
https://gitlab.com/gitlab-org/gitlab-ce/issues/32086 but seeing this pop
up again

Add info about artifacts object storage in docs

See merge request !12208

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/33598

Don't display comment on unchanged line on both sides in parallel diff

Closes #33864

See merge request !12275

Disable fork button on project limit

Closes #25164

See merge request !12145

repository: index submodules by path

See merge request !10798

Put an upper limit on update batches

See merge request !12265

Reduce wait timings for Sidekiq jobs

See merge request !12270

If migrations are pending, make CurrentSettings use existing values and populate missing columns with defaults

master was failing because `ApplicationSetting.create_from_defaults` attempted
to write to a column that did not exist in the database. This occurred in a
`rake db:migrate` task, which was unable to perform the migration that would
have added the missing column in the first place.

In 9.3 RC2, we also had a bug where password sign-ins were disabled because
there were many pending migrations. The problem occurred because
`fake_application_settings` was being returned with an OpenStruct that did not
include the predicate method `signup_enabled?`. As a result, the value would
erroneously return `nil` instead of `true`. This commit uses the values of the
defaults to mimic this behavior.

This commit also refactors some of the logic to be clearer.

This reverts commit ad521bde, reversing
changes made to 3a38e5f1.

Ensures default user limits when external user is unchecked

Closes #30725

See merge request !12218