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

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

Add option to disallow users from registering any application to use GitLab as an OAuth provider

Addresses internal issue https://dev.gitlab.org/gitlab/gitlabhq/issues/2264.

![Screen_Shot_2015-05-29_at_13.30.11](https://gitlab.com/gitlab-org/gitlab-ce/uploads/300f8e9ecbeb3d353ebc33a63cdef4e9/Screen_Shot_2015-05-29_at_13.30.11.png)

See merge request !742

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>

User should be able to leave group. If not - show him proper message
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !743

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>

Shorten merge request WIP text.

![Screen_Shot_2015-05-29_at_11.37.46](https://gitlab.com/gitlab-org/gitlab-ce/uploads/5853d9057103bdaacded17798378f68e/Screen_Shot_2015-05-29_at_11.37.46.png)
![Screen_Shot_2015-05-29_at_11.37.49](https://gitlab.com/gitlab-org/gitlab-ce/uploads/be96ee32ab5a8f23835dc37306259b17/Screen_Shot_2015-05-29_at_11.37.49.png)

See merge request !741

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

Add SAML support via Omniauth

Split of !669, with doc

See merge request !722

Include location.search and location.hash in URL for replaceState

Forgot these 😊

See merge request !740