Use SqlAlchemy for ORM instead of psycopg2

[sovaa]

The project is currently tightly coupled to psycopg2. It should be decoupled and the business logic should depend on SqlAlchemy instead. This leads to:

• unit tests can be written,
• participants can depend on a versioned module for local calc of consistency and concordance.

Currently what many are doing is they copy-paste the methods into their project, since their models likely doesn't depend on postgres. Thus fixes/changes to this repo will not be synced to peoples models or 3rd-party tools.

Unit tests can't be written easily since psycopg2 is used directly. If SqlAlchemy is used an in-memory/sqlite driver can be chosen instead, without affecting the business logic.