Create and edit files in web editor via rugged

- [x] create file via rugged
- [x] update file via rugged
- [x] remove file via rugged
- [ ] fix tests
- [x] remove satellites code
- [x] create activity event for new/edit file via rugged
- [x] base64 support

Part of https://dev.gitlab.org/gitlab/gitlabhq/issues/2300

See merge request !751

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

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

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

Fix link_to_gfm with only a reference having the incorrect link

Before:

```ruby
link_to_gfm("#4", "/foo")     # => "<a href="/namespace/project/issues/4" class="gfm gfm-issue">#4</a>"
link_to_gfm("See #4", "/foo") # => "<a href="/foo">See </a><a href="/namespace/project/issues/4" class="gfm gfm-issue">#4</a>"
```

After:

```ruby
link_to_gfm("#4", "/foo")     # => "<a href="/foo">#4</a>"
link_to_gfm("See #4", "/foo") # => "<a href="/foo">See </a><a href="/namespace/project/issues/4" class="gfm gfm-issue">#4</a>"
```

Closes #192
Closes #1721
Closes [GitHub #7115](https://github.com/gitlabhq/gitlabhq/issues/7115)

See merge request !739

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

Add an option to automatically sign-in with an Omniauth provider

Split of !669 as requested

This is useful when integrating with existing SSO environments and we want to use a single Omniauth provider for all user authentication.

See merge request !723

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

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

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

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

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

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

Refactor header css/html

* Fixes UI issue with header on zoom
* Replace duplicate numbers with variable
* Better names for css classes
* refactor header views

Fixes #1640

See merge request !750

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

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

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

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

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

Explain gitlab forks in Gemfile
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixes https://dev.gitlab.org/gitlab/gitlabhq/issues/2358

See merge request !749

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

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

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

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

Disable changing of the source branch in merge request update API

As noted in: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/738#note_1307284

See merge request !745

Allow to configure a URL to show after sign out

Split of !669 as requested

This is especially useful with SAML ( !722 ) since the omniauth-saml gem does not support single log-out. This provides a way to log out the user from the SAML IdP after signing out from GitLab.

See merge request !725

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

small typo

See merge request !747

Fix misplaced changelog entry for SAML support

See merge request !746

Add an option to automatically sign-in with an Omniauth provider without showing the GitLab sign-in page

This is useful when integrating with existing SSO environments and we want to use a single Omniauth provider for
all user authentication.

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

Add ability to leave project
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !744

Support editing target branch of merge request

### What does this MR do?

This MR makes it possible to edit the target branch of a merge request and adds a system note when this happens.

### Why was this MR needed?

Because lots of people requested this feature. :)

### Screenshots

**Edit MR page**

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/9b3d405bf7b5f945e35bae3534c2b67b/image.png)

**New MR page**

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/3657a2a9efad6d10e8470637d1166bdb/image.png)

**System note**

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/cc8066f3d3bdf09c0cce27193210567d/image.png)

### What are the relevant issue numbers?

* Closes https://github.com/gitlabhq/gitlabhq/issues/7105
* See: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/130!

See merge request !738