Switch to using migrations

@wedaly, @talbs, @stephensanchez, @jrbl: Switching us to use migrations to play nicely with the LMS now that the schemas are a little more settled. You know the drill, folks. This means that your initial database setup command now looks like: `/manage.py syncdb --migrate` and that updating your database to the latest changes is `./manage.py migrate`.

It also means that you have to generate a migration whenever you do a change to the model, via ` ./manage.py schemamigration <app_name> --auto`

I'm just tossing in the auto-generated migrations. We'll go back and do a proper look at adding composite indices later.