+ Added aurweb.models.user.User class. This is the first example
of an sqlalchemy ORM model. We can search for users via for example:
`session.query(User).filter(User.ID==1).first()`, where `session` is
a configured `aurweb.db.session` object.
+ Along with the User class, defined the AccountType class.
Each User maintains a relationship to its AccountType via User.AccountType.
+ Added AccountType.users backref.
Signed-off-by: Kevin Morris <kevr@0cost.org>
