Fix nonatomic database update potentially causing project star counts to go negative

The `counter_cache` decrement function is called when a project star is deleted,
but there was no guarantee multiple workers would not attempt to delete the
same item simultaneously. Use an atomic update to prevent the count from going negative.

Note: I was only able to duplicate the issue on GitLab.com, but I haven't been able to replicate it anywhere else. Presumably this bug happens when the `WHERE` clause takes some time to search for the right entry and multiple requests get sent simultaneously. Need to verify whether this fix truly solves the issue.

Closes #3067

See merge request !1628

Separate rendering of Markdown reference links from redacting those the user doesn't have access to and extracting referenced objects

Related: !1014

See merge request !1090

Temporary bring /ci page page with help information
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1630

Redirect old CI project route to GitLab project
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1629

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

Hide Builds tab is GitLab CI is not enabled
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1627

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

The counter_cache decrement function is called when a project star is deleted,
but there was no guarantee multiple workers would not attempt to delete the
same item simultaneously. Use an atomic update to prevent the count from going negative.

Closes #3067

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

Allow dashboard and group issues/MRs to be filtered by label

See merge request !1591

Fix import from SVN link

See merge request !1617

See merge request !1623

Use gitlab-git-http-server 0.3.0 for GitLab 8.1

See merge request !1605

This adds indexes for the following columns:

* notes.line_code
* ci_projects.gitlab_id
* ci_projects.shared_runners_enabled
* ci_builds.type
* ci_builds.status

Track compatible gitlab-git-http-server version

The 'git archive' changes in GitLab 8.1 require a version of
gitlab-git-http-server that is incompatible with GitLab 8.0, so we
need to keep track of this now.

See merge request !1603

Improve typography



See merge request !1622

Dont put padding on typography but on holder elements instead
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixes wrong padding of wiki content. 


cc @JobV @skyruler 

See merge request !1620

Make selectbox options more compact
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1619

Highlight comment based on anchor in URL
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix for #2954 

See merge request !1618

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>

Add index on ci_commits.gl_project_id



See merge request !1616

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

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

Fixes #3086

Show last commit from default branch on project home page

Implements #2705 

Screenshot: 

![Screenshot_2015-10-15_19.03.29](https://gitlab.com/gitlab-org/gitlab-ce/uploads/ef1cfa6764ab0ec5e7584ae61980a47d/Screenshot_2015-10-15_19.03.29.png)
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

cc @skyruler 

See merge request !1610

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

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

Add a system note and update relevant merge requests when a branch is deleted or re-added

If a branch is deleted with an open merge request, amended offline, and then pushed again,
GitLab doesn't bother to update the merge request even though the last commit ID and/or
code may have changed. This MR ensures that each push will update any relevant merge
requests and adds a system note if this happens as well.

The new messages look like:

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/6581eea069cd8e485b7fa4187ed4c043/image.png)

Closes #2926 

See merge request !1601

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