add 'Link' header for API response
Add button for removing source branch for merged MR's.
Changed sudo by su -c

The sudo command needs a tty to run. If you put this file on a CentOS 6, for example, it will not run in the host startup process. Instead, the 'su -c' runs the command apart if it has or not a tty.

I tested this change in a fresh install of gitlab on a CentOS 6.5 with successful.
Fix searching by extern_uid for LDAP to be case-insensitive
Fix misleading comment
Remove the email subject prefix

This changes email subjects from:

    GitLab | Team / Project | Note for issue #1234

to:

    Team / Project | Note for issue #1234

Rationale:

* Emails should be as meaningful as possible, and emphasize content over
chrome. The "GitLab" name is more chrome than content.

* Users can tell an email coming from GitLab by the sender or the header
in the email content.

* An organization that works mainly with GitLab knows that
every SVC email comes from GitLab. For these organizations, having
"GitLab" in front of every email is just noise hiding the meaningful
information.
Don't write the project namespace in email subjects

For instance, the email "Subject" field changes from:

    Mattt / Ground Control | Saving issue doesn't work sometimes (#1234)

to:

    Ground Control | Saving issue doesn't work sometimes (#1234)

Rationale:

* Most people are receiving email notifications about a single fork:
the project activity, issues and merge requests are happening either
in a root repository or in a fork, but less often in several forks.

* It removes noise from the email subject. The namespace of the project
can still be read in the email body.

* For Entreprise users that have a single namespace "MyEntreprise",
having this repeated in every email subject is very noisy.
Write the issue/merge request title in the notification email subject

This changes the email subjects for issues and merge request
notifications from:

    Team / Project | Note for issue #1234

to:

    Team / Project | Saving issue doesn't work sometimes (#1234)

Rationale:

* Scan the subject of the email notification more easily when catching
up with a lot of notifications. Instead of having to open the email to
get the title of the issue or merge request, one can simply read the
subject of the email.

* Group messages by subject: email clients will group emails in threads
if they have the same subject.
Send emails from the author

This changes the email "From" field from "gitlab@example.com" to either:

* "John Doe <gitlab@example.com>" if the author of the action is known,
* "GitLab <gitlab@example.com>" otherwise.

Rationale: this allow mails to appear as if they were sent by the
author. It appears in the mailbox more like a real discussion between
the sender and the receiver ("John sent: we should refactor this") and
less like a robot notifying about something.
Fixed attachment identifier displaying underneath note text
Also expose username for the /discover endpoint

Fixes #6328
Added executable file permission to binstubs
Update merge_request_observer_spec.rb
Bumped the gitlab_git gem version
Added the contribution guide notice

This is shown at the creation of new issues and new merge requests, when
the repository has a contribution guide file.
Add button for toggling inline comments in diff view.

This is useful when there are many comments and they're becoming a distraction when trying to read the diff.
Blob and tree gfm links to anchors work.

Fixes #6046
Remove dir prefix and suffix from tests inside dir.
Added Piwik support
Fix another instance of "created at"

Replace it with "created on".

Change-Id: Ibd26bf82d2e64f142a4f3be6da7701e5b035602f