Extract parts of LegacyDiffNote into DiffOnNote concern and move part of responsibility to other classes

Fixed issue with build auto-refresh not working

## What does this MR do?

Due to the `.json` at the end of the build URL fetch, the page wont correctly auto-reload the build log. This fixes that.

See merge request !5110

Get rid of pluralize on stage names

## What does this MR do?
Removes `pluralize` from stage names

## What are the relevant issue numbers?
Closes #18283   
Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/18920

## Screenshots (if relevant)
![Screen_Shot_2016-07-06_at_11.11.39_AM](/uploads/b1b2dd00dc8aacc6dff40cab1fe1ecdd/Screen_Shot_2016-07-06_at_11.11.39_AM.png)

cc @ayufan 


See merge request !5117

Added 100% width to open dropdown menus on mobile

## What does this MR do?

Sets dropdown-menus to be 100% width on small screens.

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

Do we want this on all dropdown menus or only dropdown menus activated by full-width buttons?
/cc @dzaporozhets 

## Why was this MR needed?

Mobile UX.

## What are the relevant issue numbers?

Closes #18858.

## Screenshots (if relevant)

![Screen_Shot_2016-06-22_at_00.14.09](/uploads/bd61721896bfac8af951374c2547acd6/Screen_Shot_2016-06-22_at_00.14.09.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
- [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 !4844

[ci skip]

Fix erroneous YAML spacing in LDAP configuration

## What does this MR do?

Fix erroneous indentation in LDAP example configuration

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

Is the indentation correct now? 😂 

## Why was this MR needed?

Bad configs in docs suck.

See merge request !4326

Fix importer for GitHub Pull Requests when a branch was reused across Pull Requests

Closes #17766

## What does this MR do?

GitHub importer fails when a repository has two Pull Requests, with the same branch name and different SHA, one of which was closed without merging, and one which is open or was merged in. This happens because we only checks if the branch exists in the [Gitlab::GithubImport::BranchFormatter#exists?](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/github_import/branch_formatter.rb#L6-8), before creating the missing references on Github. With this MR we check if both branch, and SHA exists in the current project. If no, we create the missing reference on GitHub before import the PR.

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

Nope.

## Why was this MR needed?

Github importer will fail if branch was reused across Pull Requests.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/19439

/cc @royaldark @thomasjachmann

See merge request !5103