Migrations: Fix frozen models and complete_apps

This allows to create migrations again using:

schemamigration accounts --auto
Migrations: Alter migration to depend on migration 0002 from accounts
Migrations: accounts.User now inherits from PermissionsMixin
sauq
Migrations: Now accounts.User inherits from PermissionsMixin
Migrations: Drop table for voting

Followup for c977e615.
squa
UNDO    more migrations to add