Add canceled CI status

Fixes https://github.com/gitlabhq/gitlab-ci/issues/564

https://dev.gitlab.org/gitlab/gitlab-ci/issues/169

![Screen_Shot_2015-03-19_at_17.10.08](https://dev.gitlab.org/gitlab/gitlabhq/uploads/87f47d9fd1b1a60e0c5402eedd1a1566/Screen_Shot_2015-03-19_at_17.10.08.png)

See merge request !1729