Issue boards

## What are the relevant issue numbers?

- Issue: #17907 
- Issue backend: #20335 
- Backend MR: !5548
- Frontend MR: !5554
- Documentation !5713 

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [X] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [X] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [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)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5548

Fix diff comments inverted toggle bug

## What does this MR do?
Explicitly set the comments visibility toggle based on the `active` css class.

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Fixes existing UI bug

## What are the relevant issue numbers?
Closes #20898 

## Screenshots (if relevant)
Before:
![A1ccIDEWsI](/uploads/21175e2008ee4e00225c22afebd873aa/A1ccIDEWsI.gif)

After:
![jHoFp69mAK](/uploads/e85f429d60a4e56d588faec51cd8648a/jHoFp69mAK.gif)

## 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)

See merge request !5818

Tracking of custom events

## What does this MR do?

This MR adds the ability to track custom events such as the number of Git pushes.

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

The usual stuff.

## Why was this MR needed?

We want to track more business level data such as the number of Git pushes, how many repositories are imported (and from where), etc.

## What are the relevant issue numbers?

gitlab-org/gitlab-ce#13720

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [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 @pcarranza 

See merge request !5830

Issue boards UI

## What does this MR do?

UI for issue boards.

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

## Why was this MR needed?

## What are the relevant issue numbers?

-  Issue: #17907
-  Backend MR: !5548
-  Frontend MR: !5554
- Documentation !5713 

## Screenshots (if relevant)

![Screen_Shot_2016-08-17_at_14.06.06](/uploads/e2abed987d2c2d280e8b8034c8949024/Screen_Shot_2016-08-17_at_14.06.06.png)


See merge request !5554

# Conflicts:
#	app/controllers/projects/merge_requests_controller.rb

Resolve "Pipelines for merge request"

## What does this MR do?
Adds `Pipelines` tab in merge request view

## What are the relevant issue numbers?
Closes #18681 

## Screenshots (if relevant)
![Screen_Shot_2016-08-16_at_3.22.41_PM](/uploads/c04febab3765b1fac2bf3bbfb9882f9f/Screen_Shot_2016-08-16_at_3.22.41_PM.png)

See merge request !5485

Eliminate unneeded calls to Repository#blob_at when listing commits with no path

See merge request !5848

It wasnt testing what it was saying it should be...

removed duplication

Fixed JS tests