Models

PR for code review 

Just laying out the foundation. I think this is enough for now to start making some APIs. Responsibilities and more attributes will be pushed to the models as we go along.
Alright. My bad, got used to Coursera/Udacity.
Let's put this into context of local (ph) educational system. I'll group `Students` into `Sections`. 
How about we rename `Course` into `Subject`?