Add Rails backend

[gkaemmer]

Sorry for the very large MR -- this is a pretty substantial change to the format of this repo.

What I'm thinking we should do is:

• Rename this repository gitclub-sqlalchemy-flask-react -> gitclub
• Merge this MR which adds a rails backend
• In a separate MR, add a centralized integration test suite which runs and tests all backends against a common spec.

Much of these additions are Rails boilerplate. What I'd appreciate a look at is the Rails readme and the oso initializer.