Merge branch 'implement-new-gitlab-colors' into 'master'

Add new GitLab colors

After this merge request all css must use variables for colours.

![7Od6vP7usJ__1_](https://gitlab.com/gitlab-org/gitlab-ce/uploads/01dd327770f25c76448a5860a76e34c9/7Od6vP7usJ__1_.png)
 
cc @skyruler 

See merge request !1542