Gitlab CI merge request service

This is a first implementation of exposed entrypoint to build gitlab ci service to integrate PHPCI as CI server.

Actually I have JSON conversion into Gitlab class, maybe will be better have a more generic helper to allow all type of build to be converted on JSON. Before I implemented it on controller and after moved on ```PHPCI\Model\Build``` but I'm not sure is a good place to store this conversion. Maybe a new helper class? Any suggestion?

I think is required a token to allow information reading without expose project information as public.

Test are required, please do not merge, just use this MR as support request :smile:.

Next steps:

 - [ ] define better solution to convert build to JSON
 - [ ] introduce a validation token to allow non public project to be read
 - [ ] add tests
 - [ ] implement phpci_ci_service similar to [gitlab_ci_service](https://github.com/gitlabhq/gitlabhq/blob/master/app%2Fmodels%2Fproject_services%2Fgitlab_ci_service.rb)