Add support for cross project references for labels
## Summary
Support for cross project references for labels.
## Rationale
1. Cross project label references are currently not supported in GitLab
1. `to_reference` method signature in `Label` model breaks the abstraction introduced in `Referable`.
`concerns/referable.rb: def to_reference(_from_project = nil)`
Signatures:
```
label.rb: def to_reference(format = :id)
commit_range.rb: def to_reference(from_project = nil)
commit.rb: def to_reference(from_project = nil)
external_issue.rb: def to_reference(_from_project = nil)
group.rb: def to_reference(_from_project = nil)
issue.rb: def to_reference(from_project = nil)
merge_request.rb: def to_reference(from_project = nil)
milestone.rb: def to_reference(from_project = nil)
project.rb: def to_reference(_from_project = nil)
snippet.rb: def to_reference(from_project = nil)
user.rb: def to_reference(_from_project = nil)
```
This MR suggests using `def to_reference(from_project = nil, format: :id)` which makes use of keyword arguments and preserves abstract interface.
1. We need support for cross project label references when we want to move issue to another project
It may happen that issue description, system notes or comments contain reference to label and this reference will be invalid after moving issue to another project and will not be displayed correctly unless we have support for cross project references.
Merge request that needs this feature: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2831
I think that cross project label references may be useful, (example: `Hey, see our issues for CI in GitLab CE! - gitab-org/gitlab-ce~"CI"`).
cc @JobV @DouweM @rspeicher
See merge request !2966
Indicate when an MR diverged from the target branch
This adds an indicator to the "Merge MR" box, to tell if and how much an MR diverged from its target branch.
For instance, consider an MR to merge the branch `feature` into `master`. Some other commits were added to `master` since `feature` was created, and the two branches diverged.
```text
o master
|
o o feature
| |
o o
| /
o
```
In this case, there will be a label in the MR Merge box stating:
> This MR is by 3 commits behind the target branch `master`.
## Screenshots
### The branch diverged from the target (UI Proposal)

### The branch diverged from the target (alternative UI Proposal)

## How is this useful?
- In a _rebase-workflow_ (MR are preferably rebased before being merged), the reviewer wants to know if an MR is rebased on the target branch before merging it.
_With this indicator, the reviewer knows immediately if the branch is rebased, or if she needs to ask the committer to rebase its branch._
<br>
- To keep the git history readable, a team prefers to avoid merging branches that really lag a lot behind the target branch. Merging an MR that is 10 commits behind is fine, but 200 is too much.
_With this indicator, the reviewer can see on the MR page if the branch is really far behind the target – or only a few commits behind._
## Open questions
We've been using this at @captaintrain for a few months now, and found it quite useful.
I guess the open-questions are mostly: what UI would be the more adequate? Any thoughts on this, on the general usefulness and/or on the code?
See merge request !2217
Add a spec for WikiPipeline
Removes the specs from GollumTagsFilter that were more like integration
tests for the pipeline than unit tests of the filter.
See merge request !3054
Flush repository caches before renaming projects
This should hopefully solve gitlab-org/gitlab-ce#13790. Once I know the exact steps to reproduce the problem I should be able to confirm this.
cc @dblessing @inem
See merge request !2974
Reuse query from ProjectsFinder to get projects accessible to current user.
Fixes#13648
This is a refactor to reuse the existing query from our `ProjectsFinder` class
See merge request !3049
Fix permissions for deprecated CI build status badge
This fixes permissions for deprecated status badge, being unavailable even if project is public.
Closes#13324
See merge request !3030
Return empty array when commit has no statuses in API
This makes API endpoint for Commit Statuses return empty array instead
of 404 when commit exists, but has no statuses.
Closes#3080
See merge request !3010
Don't show any "2FA required" message if it's not actually required
Prior, if the user had enabled and then disabled 2FA, they would be
shown a "You must enable Two-factor Authentication for your account."
message when going back to re-activate it, even if 2FA enforcement was
disabled.
See merge request !3014