Rename SlackNotificationService back to SlackService

## What does this MR do?

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8191#note_20310845

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/25843

/cc @yorickpeterse @stanhu @smcgivern @felipe_artur @ayufan

See merge request !8208

Resolve "Direct link from pipeline list to builds"

## What does this MR do?
- Adds a dropdown with builds in the mini pipeline graph in the pipelines table
- Unnest a lot of CSS related with pipelines in order to make it reusable

## Screenshots
![Screen_Shot_2016-12-15_at_14.45.41](/uploads/ca1c61842a422a34383e029d668034b7/Screen_Shot_2016-12-15_at_14.45.41.png)
![Screen_Shot_2016-12-15_at_14.45.49](/uploads/952e3277143639ce4ad111103034faeb/Screen_Shot_2016-12-15_at_14.45.49.png)
![Screen_Shot_2016-12-15_at_14.46.02](/uploads/f7369a124b1c3c0db4194de2cb637ef0/Screen_Shot_2016-12-15_at_14.46.02.png)

![graph_animation](/uploads/9bae036cb5acff499f992a4722943d72/graph_animation.gif)

## 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
  - [x] 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)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #25071 
Closes  #19703 

See merge request !8097

Fix N+1 queries on milestone show pages

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/25832

See merge request !8185

Changes after review