Switch to custom Models, stop using SQLAlchemy

- SQLAlchemy is too... Javaish, tries to do everything
- We have at most 4 models, no need to use a heavyweight ORM
- DDL SQL is now specified in an SQL file
- Use oursql rather than mysql-python

Change-Id: I6c5d46e56e707b431bce4df723035d83b14d8045