Use just SQL to check is a user can admin_issue on a project

Tradeoff

- we duplicate how we check admin_issue in a SQL relation in the Ability class

Fix error message for existing labels in right sidebar.

## What does this MR do?
Fixes flash notification in right sidebar, if we want to create an existing label.

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

## Why was this MR needed?
Because it was broken.

## What are the relevant issue numbers?
Fixes #20117 

## Screenshots (if relevant)

#### Before
![https://gitlab.com/gitlab-org/gitlab-ce/uploads/c1fa7e98d1a3f0daaf8197809bbb26d0/Screen_Shot_2016-07-22_at_11.33.35.png](https://gitlab.com/gitlab-org/gitlab-ce/uploads/c1fa7e98d1a3f0daaf8197809bbb26d0/Screen_Shot_2016-07-22_at_11.33.35.png)

#### After
![Screen_Shot_2016-07-28_at_13.38.03](/uploads/1dca73bf4c1b14c0044952a5032d9325/Screen_Shot_2016-07-28_at_13.38.03.png)
![Screen_Shot_2016-07-28_at_13.41.18](/uploads/9b814f7f03d0314050659e1ac6ace290/Screen_Shot_2016-07-28_at_13.41.18.png)

## Does this MR meet the acceptance criteria?

- [x] [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~~
  - [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 !5546

Don't show comment button in gutter of diffs on MR discussion tab

When browsing to an MR, switching to the Changes tab, and switching back to the Discussions tab, the gutter of the diffs on that page would show the comment button on-hover, while it shouldn't, since comments on new lines can only be created from the Changes tab.

![Screen_Shot_2016-07-25_at_22.01.11](/uploads/6b044e1a3ecb34ddaa0af432833473aa/Screen_Shot_2016-07-25_at_22.01.11.png)

`8-10-stable` counterpart at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5493

See merge request !5492

Changed project description width

## What does this MR do?

Changes the width of the project description to a max of `700px`

## What are the relevant issue numbers?

Closes #20020 

## Screenshots (if relevant)

![Screen_Shot_2016-07-21_at_12.51.59](/uploads/567f5b11553b45baa7fb07156e46b727/Screen_Shot_2016-07-21_at_12.51.59.png)

See merge request !5397

Implement pipeline hooks, extracted from !5525

Closes #20115

See merge request !5620

Highlight empty lines

## What does this MR do?

Rather than just highlight the text, file line highlighting now highlights the full line including empty lines

## What are the relevant issue numbers?

Closes #19484 

## Screenshots (if relevant)

![Screen_Shot_2016-07-05_at_13.52.31](/uploads/d3bddc918d731681465381e96c0aa2b0/Screen_Shot_2016-07-05_at_13.52.31.png)

See merge request !5092

Load issue templates from repository

part of #18656 


## 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)

See merge request !4981