Move Features to Nasqueron\Notifications\Config namespace
Summary:
The Nasqueron\Notifications\Config will contain any class about
configuration. It has been imagined during D785 / T1066.
Test Plan: Adapt test, then run them
Reviewers: dereckson
Reviewed By: dereckson
Subscribers: alken-orin
Differential Revision: https://devcentral.nasqueron.org/D786