New doc about creating a Merge Request in GitLab Basics

Added new doc about creating a new branch.

See merge request !1917

Allow custom backup archive permissions

This change helps system administrators who want to replicate
GitLab backup files without needing root permissions.

See merge request !1888

Experimental support for gitlab-git-http-server

https://gitlab.com/gitlab-org/gitlab-git-http-server

This change introduces the GITLAB_GRACK_AUTH_ONLY environment
variable. When set, Grack requests to GitLab will only respond with
the user's GL_ID (if the request is OK) or an error. This allows
gitlab-git-http-server to use the main GitLab application as an
authentication and authorization backend.

If we like how this works we should drop the GITLAB_GRACK_AUTH_ONLY
variable at some point in the future.

See merge request !1915

Switch back to rouge gem for synthax highlighting

Since gollum-lib blocks rouge from updating, let's bump the version
manually. The fix has already been accepted upstream:
https://github.com/gollum/gollum-lib/commit/9c042ea0914a7714abbda9d89e234c8a79fba893

This custom formatter for rouge is needed to generate HTML output
specifically for gitlab. Since its usecase is mostly suitable for
gitlab it had been rejected upstream:
https://github.com/jneen/rouge/pull/268

Thanks a lot to @stanhu, @jneen and @tsigo for review!

I have mainly created the rugments fork for the purpose of improving
gitlab's highlighting. Nowadays IMO it works way better than the old
highlight.js solution. But the development is stuck on my side because
of a couple of personal reasons:

  * I have finished my studies; last months I was writing my master
    thesis. So there was a huge time problem. I am sorry for that.

  * I had to move to Munich due to getting a (paid) job. Searching a
    flat here is horrible... :)

  * Last but not least, maintaining the same code base in two seperate
    projects is a mess.

I have decided to switch back to rouge due to several reasons:

  * In the beginning I was quite motivated, but since I start
    working on my new job next week, the best solution IMO is
    switching back to upstream rouge.

  * Rouge is continously improving:
    https://github.com/jneen/rouge/blob/master/CHANGELOG.md
    http://rouge.jneen.net/

  * There should be absolutely no regressions with this change. Most
    likely this pull request will almost fix some minor bugs.

  * One less gem in gitlab is a good thing. since Gitlab is quite a
    huge bundle of gems. Reducing complexity should be a major
    milestone.

Thanks a lot to @stanhu and @jneen for the review!

Make `hr`s more visible in note bodies

Closes #2107

See merge request !1054

Fix bug causing Bitbucket importer to crash when OAuth application
had been removed.

Fixes gitlab-com/support-forum#241.

See merge request !1057

Change before(:all) -> let! to avoid leaking data across tests

Closes https://github.com/gitlabhq/gitlabhq/issues/9495

See merge request !1061

Closes https://github.com/gitlabhq/gitlabhq/issues/9495

Upgrade gitlab_git to version 7.2.6 to fix 500 Error when creating network graphs

See merge request !1060

Closes #745

To make Rubocop and Douwe happy

Added a timestamp to the wikis page just below the title

Now it looks like this:

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/813f85496db915cf14ee223c8b15478f/image.png)



See merge request !1055

New document in GitLab Basics about adding new files



See merge request !1913

Added info about repo size

Because of tweet https://twitter.com/s_hulard/status/624160758335672320

See merge request !1912

https://gitlab.com/gitlab-org/gitlab-git-http-server

This change introduces the GITLAB_GRACK_AUTH_ONLY environment
variable. When set, Grack requests to GitLab will only respond with
the user's GL_ID (if the request is OK) or an error. This allows
gitlab-git-http-server to use the main GitLab application as an
authentication and authorization backend.

If we like how this works we should drop the GITLAB_GRACK_AUTH_ONLY
variable at some point in the future.

Return comments in created order in merge request API

Closes #1832

See merge request !985

Fix commit data retrieval when branch name has single quotes

Quotes in ref names need to be escaped properly in JavaScript.

Closes #1724

See merge request !1046

Render Note field hints consistently for "new" and "edit" forms

- The "Edit" form didn't have Markdown hints.
- The "New" form had a paperclip icon for attachments, the "edit" form
  didn't.

Closes #2010

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2525

See merge request !1049