A simpler implementation of finding a merge request

## What does this MR do?

This cleans up some code in the issues API as discussed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7180#note_19501743

The helper method `merge_request_for_resolving_discussions` was no longer needed as it was only used once. That made it possible to simplify the implementation.

## Does this MR meet the acceptance criteria?

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

!7180

See merge request !7955

Remove more pages css

* Moves award emojis to `/framework`
* Moves generic image styles to `/framework`
* Removes `confirmation.scss`

See merge request !7952

Remove dashboard.scss

See merge request !7960

# Conflicts:
#   app/assets/stylesheets/framework.scss

Remove tags.scss

Remove `tags.scss`

See merge request !7935

Remove admin.scss

Removes admin-specific CSS

See merge request !7932

Following a discussion in !7180

Encourage bug reporters to mention if they use GitLab.com [ci skip]

See merge request !7954

Explain "js: true" in "deleted_source_branch_spec.rb"

See merge request !7949

Create an issue for all unresolved discussions in an MR

See merge request !7180

Fix Archived project merge requests add to group's Merge Requests

Closes #24733

See merge request !7790

Guests can read builds if those are public

See merge request !6842

Refine CI Statuses

## What does this MR do?

This MR introduces classes for each relevant CI status.

## What are the relevant issue numbers?

Closes #24273

See merge request !7889

Use `--extended-regexp` in lint-doc for compatibility with Darwin grep

Now it should work on all platforms.

See merge request !7943

GLM shorthand reference for projects from the same namespace

Closes #21679

See merge request !7255

Authorize users into imported GitLab project

https://gitlab.com/gitlab-com/support-forum/issues/1313

See merge request !7936

Fixed MR widget content wrapping for XS viewports

Centers the "Accept Merge Request" button within the MR widget (and adds a bit of right/left padding) for viewports smaller than 768px.

BEFORE:
![Screen_Shot_2016-12-02_at_8_53_01_AM](/uploads/fcdae5302a1407090483dd3cff868c51/Screen_Shot_2016-12-02_at_8_53_01_AM.png)

AFTER:
![Screen_Shot_2016-12-02_at_9_43_37_AM](/uploads/f7d1dce082b79d263f05cea3c90e870a/Screen_Shot_2016-12-02_at_9_43_37_AM.png)

cc: @markglenfletcher @annabeldunstone 
Closes #25202

See merge request !7900

Ensure state param has a valid value when filtering issuables.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/25064

This fix makes sure we only call safe methods on issuable when filtering by state.

See merge request !2038

Document the public Project API and document `GET /projects/:id/users`

Documentation was not updated in !7843. Also the `GET /projects/:id/users` endpoint was not documented at all!

See merge request !7897

Remove unused errors css

`.error-page` isn't being used anywhere as far as I can see so I removed it

See merge request !7933

Remove unused votes.scss

`.votes-inline` isn't being used anywhere

See merge request !7934

NIGNX -> Nginx

This shouldn't be in all caps, and it should be spelled correctly!

See merge request !7929