Resolve Merge conflicts in editor

## What does this MR do?

This is the second iteration of https://gitlab.com/gitlab-org/gitlab-ce/issues/20344 which now allows to resolve conflicts manually providing an editor to the user.

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

- Previous implementation has been refactored almost from the ground up.
- Also some components like `parallel-conflict-lines` has been optimized to work well with PhantomJS.
- The app and files required files are loaded only when needed. `merge_conflicts_bundle.js` is only loaded in `/<group>/<project>/merge_requests/<Id>/conflicts` only

## Why was this MR needed?

Some MRs were unable to be solved interactively in the UI, with this MR we let the user to manually fix complex merge request conflicts.

## Screenshots (if relevant)

<img src="/uploads/33a016f025bd590b1fc6eeee1ee11626/Screen_Shot_2016-09-19_at_1.39.39_PM.png" width="800">

## 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
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] 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)
- [ ] [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/20344, https://gitlab.com/gitlab-org/gitlab-ce/issues/3567.

See merge request !6374

Fixes endpoint to username validator

Fixes failing specs on master. Introduced here https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6328

See merge request !6951

Merge branch '22191-delete-dynamic-envs-mr' of gitlab.com:gitlab-org/gitlab-ce into 22191-delete-dynamic-envs-mr

Apply better hierarchy to markdown headers and issue/mr titles

## What does this MR do?
Applies better hierarchy to markdown headers and issue/mr titles

## Why was this MR needed?
Titles of issues/mr's were smaller than h1, leading to strange hierarchy when reading descriptions

## Screenshots (if relevant)

### Before:
![Screen_Shot_2016-10-14_at_1.31.37_PM](/uploads/79b6b16b8ed1b3b49578161eea1f0e42/Screen_Shot_2016-10-14_at_1.31.37_PM.png)

### After:
![Screen_Shot_2016-10-14_at_1.31.26_PM](/uploads/f710b63c112e342c5429810984079da6/Screen_Shot_2016-10-14_at_1.31.26_PM.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
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #21395

See merge request !6904

Fix toggling of expand/hide pipeline graph button

## What does this MR do?

Corrects the toggling behaviour given that the pipeline graph now starts in a different state.

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

## Why was this MR needed?

Expand/hide toggling UI is buggyyy

## Screenshots (if relevant)

![2016-10-14_18.15.41](/uploads/7cdeef02c0b8aa4266f2878866e4b633/2016-10-14_18.15.41.gif)

## 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
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #23358

See merge request !6898

Rename users routing from /u/:username to /users/:username for
consistency with other routes

Renames /u/:username to /users/:username

To follow consistency with other routes (like groups) and
UsersController name.
Now when you can use `/:username` for accessing user page there is no
need in shortcut like `/u/`

See merge request !6851

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixed find file keyboard navigation

## What does this MR do?

The code to view a file on find file page was removed, this adds that back in & adds some tests.

## What are the relevant issue numbers?

Closes #23423

See merge request !6944

Resolve "No space between buttons on Files page"

## What does this MR do?

Adds a `.download-button` class to the project download button and added `10px` of margin to this button within the `.tree-controls`.

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

## Why was this MR needed?

Whitespace is gr8!

## Screenshots (if relevant)

![Screen_Shot_2016-10-16_at_14.05.09](/uploads/2da692bd55e06c730d048ccf9173bd2c/Screen_Shot_2016-10-16_at_14.05.09.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
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #23380

See merge request !6921

Enable activerecord_sane_schema_dumper for test

## What does this MR do?
Enable `activerecord_sane_schema_dumper` for test allowing to use `test` database for consistent schema generation.

See merge request !6931

Closes #23423

Updated logo from @luke

Closes #23274

See merge request !6942

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

Merge branch '22191-delete-dynamic-envs-mr' of gitlab.com:gitlab-org/gitlab-ce into 22191-delete-dynamic-envs-mr