Merge branch '18297-i-would-like-text-to-wrap-when-in-edit-mode-on-web-app' into 'master'

Added soft wrap option to editor

## What does this MR do?

Adds a `Soft wrap` button to the editor, when clicked, it wraps the text in the editor and changes to `No wrap`, then when clicked, it unwraps the text in the editor.

This will also detect files with no extension, `.txt` or `.md` and proactively set the soft wrap. **Unless**, you explicitly toggle the soft wrap, then it will stop checking the file path and will stay with the users explicit preference.

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

We should talk about the `.txt` and `.md` thing, [I'm not sure if its a good approach](https://gitlab.com/gitlab-org/gitlab-ce/issues/18297#note_14918218).

## Why was this MR needed?

## Screenshots (if relevant)

https://youtu.be/8LW5nQsraSM

#### No wrap

![Screen_Shot_2016-09-02_at_19.54.54](/uploads/97f2d1b2d415d03fe1b0be0640ab12e0/Screen_Shot_2016-09-02_at_19.54.54.png)

#### Soft wrap

![Screen_Shot_2016-09-02_at_19.54.45](/uploads/5af425587ce7198e015cce58440971b9/Screen_Shot_2016-09-02_at_19.54.45.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 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 #18297

See merge request !6188