Refactor PhabricatorListener

Summary:
This change moves the responsibility to perform the task
from the event listener to a dedicated job class.

The job class NotifyNewCommitsToDiffusion allows to call the
Phabricator API for any repository, not only for GitHub ones.

As a preparation for T851, we provide a getPhabricatorProject
method to allow to map source project and Phabricator project.

Ref. T851.

Test Plan:

• With artisan tinker, prepare a notification for rTOMMY
• Minimal test to check job wants a Phabricator API

Reviewers: dereckson

Maniphest Tasks: T851

Differential Revision: https://devcentral.nasqueron.org/D531