New GitLab API PHP Wrapper

Summary:
Inital commit of GitLab API PHP Wrapper module.
Finished Client.php, Users.php, Projects.php.
Fixed line length warnings.
Updated the Sync GitLab module to use the new library and implemented improved error handling.
Corrected parsing JSON. Improved Exceptions. Improved docs.

Test Plan: Tested by hand.

Reviewers: m.iancu

Reviewed By: m.iancu

Differential Revision: http://phab.code4fun.de/D91