Add Pending Tab to Builds

## What does this MR do?

Add Pending Tab to Builds and separate "running" and "pending" jobs in UI.

## Why was this MR needed?

Increase visibility to "pending" .

## What are the relevant issue numbers?

Closes #19408 

## Screenshots

Before:
![Zrzut_ekranu_2016-07-05_o_11.52.48](/uploads/01dc1f3664f5aacb2ec09d52d19c521e/Zrzut_ekranu_2016-07-05_o_11.52.48.png)

After:
![Zrzut_ekranu_2016-07-05_o_11.51.34](/uploads/f3be02427996fecf50c65dd51ce1b9fb/Zrzut_ekranu_2016-07-05_o_11.51.34.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [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 you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

cc @ubudzisz @yorickpeterse @grzesiek @tmaczukin @zj [@chastell](https://github.com/chastell) [@tomash](https://github.com/tomash)

See merge request !5084