Move third-party applications from readme to website
Move the contents of https://gitlab.com/gitlab-org/gitlab-ce/blob/master/README.md#third-party-applications => https://about.gitlab.com/applications/
consider making an 'app' section and an 'api client' section
and link from the readme to https://about.gitlab.com/applications/
Also add GitLab CI and Magnum CI http://blog.magnum-ci.com/post/55149963415/integration-with-gitlab to https://about.gitlab.com/applications/