Created Gerrit Change class

Gerrit\Change will encapsulate the majority of the concerns currently housed in Gerrit\Api

The plan is for the Api to become a generic tool for dispatching calls to the Gerrit API. Actual business knowledge will live in individual "model" classes
Remove skipped test; I don't plan to fix it any time soon
Creating GitHookException and renaming some variables
Created new Git Hook to do Gerrit merges

Replaced Witness with Logger
Update bart to PHP 5.4!
PSR up ReceiveRunnerBase and family