Update DB to match proposed App Metadata Schema and Improve type safety

[francisduvivier]

Currently we are just writing sql in the routes specification directly and we don't have a lot of type safety for the things that we do with the DB.

This could be improved by putting an abstraction layer in between to protect the API logic from DB interaction logic. And then in the DB interaction logic, we can use interfaces that exactly match the DB table structure.
To be even more typesafe and in order not to repeat the database specification and typing, we could use sequelize typescript.