Unify models

[wilko77]

Yeah the double up of models modules isn't ideal. As you can tell I have avoided the large task of moving off directly using psycopg2 to using sqlalchemy in the application code.

I think the top level one could mostly be replaced by using the sqlalchemy models and using marshmallow to create the orm objects as per this example. I just don't have the time to take that on.

Originally posted by @hardbyte in #603 (comment)