Added colored labels to related MR list.

## What does this MR do?
Added colored labels to related MR list.

## Are there points in the code the reviewer needs to double check?
Yes, I think haml can be better.

## Why was this MR needed?
There was an issue for this #21200 

## Screenshots (if relevant)
![Screen_Shot_2016-11-15_at_21.04.24](/uploads/b601f33f23cdc3318d01279e17deb096/Screen_Shot_2016-11-15_at_21.04.24.png)

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Fixes !21200

See merge request !7486