These three tests were essentially checking that adding a note to
something updated its `noteable`'s `updated_at` attribute.

This is well-tested Rails behavior and we shouldn't feel the need to
write an integration test to verify it. At most we should be ensuring
that the association definition adds the `touch: true` option, which we
now do in Note's unit test.

Labels should be visible in dashboard and group milestone views

Closes #13621

See merge request !2931

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)

![UI_suggestion_1](/uploads/cd5bee3959e68026ec7d5097259d53f4/UI_suggestion_1.png)

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

![UI_suggestion_2](/uploads/f36977101b59a610850e129837dfbc83/UI_suggestion_2.png)

## 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

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