Refactor Services as a Facade to a more generic Services class

Summary:
Currently, Services were a bag of static methods to read
credentials.json.

We now provide:

• a generic and autonomous Services class
• a Service class to represent a credentials.json entry
• a services provider to register our application instance of Services
• a Services facade, as a drop-in substitute for the former Services

Test Plan:
Send a payload request.

Run commands php artisan config:show and php artisan phabricator:projectsmap.

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D180