Migration: Use uuids for acl instead of usernames

[pavog]

The account acl for bank accounts adds the ability to let other players see or control the bank account.
This is saved in the acl table and uses playernames instead of uuid.
Since you can change our usernames this might be a security vulnerability and should be changed in the near future.

Since this requires a change in the database table it should ship with an automatic migration and as a breaking change so within a new major version.