Resolve "User university issue"

Prepared database schema for enabling players from different universities. Won't work with current game server's implementation of user registration (notify @niklas.fix when deployed to dev database)

Unrelated to that issue: Players must have a valid selected title and a valid selected avatar. Furthermore, as described in https://www.rfc-editor.org/errata/eid1690 email addresses can have a maximum length of 254 characters in practice. Since verification isn't optional and unverified users are deleted regularly, we are protected from spam.

Closes #3 (closed)