Update the schema creation DDL for the new password hashing

I'm not sure whether this slipped out in a merge or whether I
forgot to add it in the first place, but it should have been part
of commit 5924533c6d0f9777d38c01ed7e1510a55db2b876.  This
completely broke setting up a new Quassel instance from scratch
with 0.12-rc1, but upgrades from previous versions are unaffected.