Provide a config module

Summary: Allow to configure the microservice.

Test Plan:
Refactored from API production code

After moving the config code to this crate:
2018-09-04T18:58:31Z: rocket::rocket: Rocket has launched from http://0.0.0.0:8000

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1664