Remove old sessions in order to force a new access_token access

/cc @vsizov @jacobvosmaer

See merge request !188

Refactoring: Get rid of private_token usage in the frontend

See merge request !185

Rounded coverage on commit page

https://dev.gitlab.org/gitlab/gitlab-ci/issues/312

See merge request !184

Change favicon

https://dev.gitlab.org/gitlab/gitlab-ci/issues/292

See merge request !183

Redirect back after authorization

https://dev.gitlab.org/gitlab/gitlab-ci/issues/287

See merge request !182

Enhance YAML validation

/cc @vsizov

See merge request !180

Update nokogiri version to remove warnings about libxml version mismatch.

GitLab [is using this version of nokogiri](https://gitlab.com/gitlab-org/gitlab-ce/blob/7-12-stable/Gemfile.lock#L378-379) too. The difference between current version and latest version is in multiple security and bug fixes as well as some features, see [their changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.rdoc).

Reason why I've created this MR is that upgrading to 1.6.6.2 removes warnings about libxml version mismatch when running ci rake tasks in omnibus as shown here: omnibus-gitlab#636 .

See merge request !179

Build status Badge: unable to obtain code

https://dev.gitlab.org/gitlab/gitlab-ci/issues/304

See merge request !177

Improved validation of .gitlab-ci.yml

https://dev.gitlab.org/gitlab/gitlab-ci/issues/305

See merge request !176

Fix list of branches in only section

https://gitlab.com/gitlab-org/gitlab-ci/issues/195

See merge request !174

Fix coverage colcalation on the commit page

See merge request !171

Implemented rake env:info

https://dev.gitlab.org/gitlab/gitlab-ci/issues/298

See merge request !172

Disable colors in rake tasks automatically

https://gitlab.com/gitlab-org/gitlab-ci/issues/164/

See merge request !166

Warning when .gitlab-ci.yml not found

https://dev.gitlab.org/gitlab/gitlab-ci/issues/295

![joxi_screenshot_1435155049429](https://gitlab.com/gitlab-org/gitlab-ci/uploads/83e34bba9bb7cb69d0fc663ee1077605/joxi_screenshot_1435155049429.png)

See merge request !164