APIClient and APIFactory contracts

Summary:
To improve dependency injection in ProjectsMap, we create two
interface contracts, APIClient and APIFactory, which abstract
an API client and a class to instantiate them.

That allow to easily inject an API client and increase components
independance.

Test Plan: A variation of fea5b9c has successfully been tested.

Reviewers: dereckson

Subscribers: alken-orin

Differential Revision: https://devcentral.nasqueron.org/D333