Support Gitlab hook

These are example messages:
![2014-11-28 16 12 06](https://cloud.githubusercontent.com/assets/290782/5224535/622c0a0a-7719-11e4-95b8-1bccf62a56bb.png)


see for details: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/web_hooks/web_hooks.md
Alternatively, we can use https://about.gitlab.com/images/gitlab_logo.png .
Which url should be used?

Or should we fetch this image?