New data layer - postgres based (with fkeys and cascading deletes)

Every model attribute also includes the appropriate validation
messages
Created some seed data
ARD - extracts data from ActiveRecord objects
Todos are cascaded destroyed by lists
List api implementation and driver
We don't need this stuff for a single page app.
Mirror database validation at the model level.

Thanks @jsconnoly
Bugfix.
Todo controller almost done. Missing delete and update.