Fix Error 500 when accessing application settings due to nil disabled OAuth sign-in sources
## What does this MR do?
When upgrading to GitLab 8.8, an admin would encounter an Error 500 due to a `nil` `disabled_oauth_sign_in_sources`. This MR ensures that the value will be a blank array if empty.
Closes#17564
See merge request !4242
Fix some specs which would have broken in 2017 to not break anymore by using a dynamic year value.
Static year values would have caused the test suite to fail on these in the future, so I replaced 'em.
That's pretty much all there is to this MR.
See merge request !4241
Allow anonymous user to access pipelines
## What does this MR do?
It fixes an issue where the Pipelines is shown for the Anonymous users,
but they get 404 when clicked. Their session is then logged out.
Fixes#17717.
See merge request !4233
Fix the CI login to Container Registry (the gitlab-ci-token user)
## What does this MR do?
This fixes `docker login` not succeeding when trying to do CI login: `gitlab-ci-token with $CI_BUILD_TOKEN`.
cc @marin
See merge request !4236
Add README for updating .gitignore templates
Add notes to make it clear that users should not file a MR against a specific file here.
See merge request !4227
Fix fork counter ui bug for safari
## What does this MR do?
Fixes UI bug on safari when fork button has blue arrow
## Screenshots

See merge request !4221
Issuable form due date
For some reason, this was never in the original merge request for due date?

Closes#15516
See merge request !3895
Fixed issue with enter key selecting wrong option in dropdown
If you search for a label and press enter the dropdown will select the last element rather than the first. This is because the currentIndex is -1 rather than 0

Closes#17630
See merge request !4210
Fixed issue with merge button color

Closes#17644
See merge request !4211
Wrap "No groups found" message with a .nothing-here-block
The "No groups found" message's style is inconsistent with the other empty messages.
## Screenshots
### Empty groups

### Empty projects

See merge request !4137