Merge remote-tracking branch 'upstream/pipeline-hooks-without-slack' into wall-clock-time-for-showing-pipeline

* upstream/pipeline-hooks-without-slack:
  Make explicit call for all event types for ProjectHook factory
  Capitalise URL on web_hooks/form
  Remove changes not related to this MR
  Added documentation for pipeline hooks
  Rename queue to enqueue in tests
  Instrument Project.visible_to_user
  Fix build play failure
  Update ruby 2.3.1
  Improve transition between states for event `enqueue`
  Use event `enqueue` instead of `queue`
  Fix test failures
  Fix bug where destroying a namespace would not always destroy projects
  Remove unused SpamReport model; this was renamed to SpamLog
  Corrected links/usernames in performance guide
  Add gravatars to build history
  Add deployment ID and gravatar to environments page
  Format environment history page
  Add avatar to commit message; environment style updates to match pipelines page
  Style deploy button