Allow to block JIRA events for commits and merge requests

implements #5541 

See merge request !7469

Remove unnecessary self from user model

self keyword nod needed. Code is more clean and understandable. https://github.com/bbatsov/ruby-style-guide#no-self-unless-required

See merge request !7551

Fixes regression causing an error message to appear when user first enters the Merge Request form.

Closes #24627

See merge request !7599

Revert signin tab order fix.

The history: 

> 1. @sytses created this: https://gitlab.com/gitlab-org/gitlab-ce/issues/23279
> 2. The fix was submitted here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6867
> 3. I [made](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6867#note_16993324) the same observation you did after it was merged
4. A long discussion about accessibility and UX followed, and we decided to revert all changes (https://gitlab.com/gitlab-org/gitlab-ce/issues/23698).

## Screenshots (if relevant)

![2016-11-17_20.55.22](/uploads/c81b0bbe0cd08747124531778af6273f/2016-11-17_20.55.22.gif)

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [x] 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?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/23698

See merge request !7538

Resolve "Display "folders" for environments"

## What does this MR do?
Adds the ability to show the grouped environments inside "folders".
Adds several reusable vue components in order to accomplish the recursive tree data structure presented.

For the individual components, Jasmine tests were added.
For the ones that depend of an API response, rspec tests are used.


## Screenshots (if relevant)
![Screen_Shot_2016-11-16_at_02.00.13](/uploads/1278012c8639b999b53f080728d283e1/Screen_Shot_2016-11-16_at_02.00.13.png)
![Screen_Shot_2016-11-16_at_02.00.25](/uploads/a3d65416ddb553e1b8f0f4c8897a75dc/Screen_Shot_2016-11-16_at_02.00.25.png)
![Screen_Shot_2016-10-17_at_16.08.50](/uploads/af63efe1d2cbd5fc069408622ef4b607/Screen_Shot_2016-10-17_at_16.08.50.png)


![environments](/uploads/b5a1801766d82ab176fc60f96b6968cb/environments.gif)
## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry 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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22539

See merge request !7015

Merge request !7163 caused an error message to appear on the Merge
Request form when it was first loaded by the user. This commit fixes
that regression bug.