Added VueJS plugin

## What does this MR do?

Adds the VueJS & Vue resource plugin with environment detection. 

## What are the relevant issue numbers?

Closes #20738 

See merge request !5845

Fix downtime check formatting

## What does this MR do?

This MR adjusts the formatting of the migration downtime checker so messages are more readable.

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

Not specifically

## Why was this MR needed?

Formatting was somewhat hard to read and the online/offline indicators used the wrong colour.

## New Format

```
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20140407135544_fix_namespaces.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160705054938_add_protected_branches_push_access.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160705054952_add_protected_branches_merge_access.rb
[offline]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160705055254_move_from_developers_can_merge_to_protected_branches_merge_access.rb:

We're creating a `merge_access_level` for each `protected_branch`. If a user creates a `protected_branch` while this
is running, we might be left with a `protected_branch` _without_ an associated `merge_access_level`. The `protected_branches`
table must not change while this is running, so downtime is required.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5081#note_13247410

[offline]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160705055308_move_from_developers_can_push_to_protected_branches_push_access.rb:

We're creating a `push_access_level` for each `protected_branch`. If a user creates a `protected_branch` while this
is running, we might be left with a `protected_branch` _without_ an associated `push_access_level`. The `protected_branches`
table must not change while this is running, so downtime is required.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5081#note_13247410

[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160705055809_remove_developers_can_push_from_protected_branches.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160705055813_remove_developers_can_merge_from_protected_branches.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160716115711_add_queued_at_to_ci_builds.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160725083350_add_external_url_to_enviroments.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160727163552_create_user_agent_details.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160728081025_add_pipeline_events_to_web_hooks.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160728103734_add_pipeline_events_to_services.rb
[offline]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160729173930_remove_project_id_from_spam_logs.rb:

Removing a column that contains data that is not used anywhere.

[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160801163709_add_submitted_as_ham_to_spam_logs.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160802010328_remove_builds_enable_index_on_projects.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160805041956_add_deleted_at_to_namespaces.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160810102349_remove_ci_runner_trigram_indexes.rb
[online]: /home/yorickpeterse/Projects/gitlab/gitlab-ce/db/migrate/20160810142633_remove_redundant_indexes.rb
```

## Does this MR meet the acceptance criteria?

- 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 !5840

This removes excessive whitespace from the messages (e.g. leading
whitespace) and ensures the message is more clearly visible.

The colours were incorrect: offline was green and online was red,
instead of the opposite.

Move to project dropdown with infinite scroll for better performance

See merge request !5828

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