Nasqueron\Notifications\Analyzers\Phabricator namespace

Summary:

• Moved Phabricatro analyzer classes to a new Phabricator namespace.
• Renamed PhabricatorGroupMapping class to ProjectGroupMapping, to be coherent with the RepositoryGroupMapping class.

Test Plan: Fire a Phabricator payload to the notifications center.

Reviewers: dereckson

Subscribers: alken-orin

Differential Revision: http://devcentral.nasqueron.org/D284