Add an Ember-data compatible API

Part of this is also updating the ember app to pull data from this API.

The current plan is to store data in a relational database using
SQLAlchemy and to access and expose that data through an Ember Data
compatible set of REST-ful endpoints under `/api`.

To that end:
 - I'm adding `Flask-SQLAlchemy` and `Flask-Migrate`.
 - I'm converting the current ember app to use Ember Data and FIXTURES
 - Once I've mocked out the data and interactions in javascript then
 I'll work to provide the necessary models in SA and the necessary
 endpoints under `/api`.

Initially it looks like the relevant models for the MVP are just:
 - League
 - Player
 - Game

I imagine there will be more that I haven't thought of but that's for
another day.