Add Initial Models, Migrations, Fixtures, and Tests

Here's the initial implementation of the data model as defined in our google doc. I've also included a few basic tests and fixtures for us to use.

User passwords are hashed and salted automatically (both values are stored together in the `password_digest` column). The `password` and `password=` getter/setter will transparently encrypt or decrypt the password as needed.

@ryanseys 
@oharaandrew314 
Insecure how? What would be insecure? If I create an account from the main page, I should be the owner of my restaurants. If not, then how do I become an owner? Sounds counterintuitive. Maybe I just don't get the "rails way" :)