Fix pipeline graph hidden on commit and mr pages

## What does this MR do?

Dynamically invokes `new gl.Pipelines();` when an MR `builds` tab is clicked.

Dispatches `new gl.Pipelines();` on a `commit#builds` page.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

The pipeline graph was hidden on commit and mr pages

## Screenshots (if relevant)

Commit page:
![Screen_Shot_2016-10-14_at_18.16.18](/uploads/ee11dea0825d1489dc167292e16c8f41/Screen_Shot_2016-10-14_at_18.16.18.png)

MR:
![Screen_Shot_2016-10-14_at_18.16.39](/uploads/602c2fce2397c799bedb757bfd3010af/Screen_Shot_2016-10-14_at_18.16.39.png)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] 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 #23325

See merge request !6895
Signed-off-by: Rémy Coutable <remy@rymai.me>