Roadmap to v2.2

We all know MongoDB isn't silver bullet, and, as ng-fullstack grows, we have to give the devs more options.

We're planning to add the following DBs to the stack:
- RethinkDB;
- PostgreSQL (via sequelize.js for nodejs and pq for Golang);
- Firebase.

This is 1.11 in short:
- [ ] RethinkDB (#158);
- [ ] PostgreSQL (#159);
- [ ] Firebase (#169);
- [ ] No DB (#171);