Abstract anything touching the DB

[chadfurman]

Rather than using Knex for everything, we should be able to implement the auth-level functionality in SQL ourselves. A couple of issues will benefit from this.

[chadfurman]

This might actually be done, looking at https://github.com/clevertech/authentication-service/blob/master/src/database

I'll think on it, though as it stands I suspect this ticket should be closed and replaced by a pg-specific database adapter.