Merge remote-tracking branch 'upstream/master' into pipeline-hooks

* upstream/master: (368 commits)
  Don't fail on an empty database
  Refactor authorization_for_merge_requests.md
  Support MySQL too, when removing gitorious from import_sources
  Remove gitorious from import_sources on ApplicationSetting model
  Add links to new docs in merge_requests.md and workflow/README.md
  Move merge request versions to its own document
  Move "Only allow merge requests to be merged if the build succeeds" to new location
  Move revert_changes.md to new location
  Move cherry_pick_changes.md to new location
  Move `wip_merge_requests.md` to a new location
  Move merge_when_build_succeeds.md to new location
  Fix missing flash messages on service edit page
  Move authorization_for_merge_requests.md to new location
  Move `workflow/merge_requests.md` to `user/project/merge_requests.md`
  Update README.md
  Fix randomly failing specs in expand_collapse_diff_spec:
  Add link on API docs index page
  Move CHANGELOG entries of !5361, !5451 and !5887 from 8.11 to 8.12
  Remove suggested colors hover underline
  Fix markdown anchor icon interaction
  ...