Migrations: accounts.User now inherits from PermissionsMixin

Followup for 4d678d8.
Migrations: Drop table for voting app

Followup for c977e615.
Migrations cleanup: Align frozen models to ease comparison
Migrations: Fix field in frozen models across migrations
Migrations: Add dependency
Migrations: Add another dependency
Migrations: Add another new dependency
Migrations: Add missing frozen models on migration
Migrations: Fix frozen models
Migrations: Fix more frozen models

Adding dependencies on other migrations allows to simplify the frozen
models. Also all the references to PootleProfile were changed in
favor of accouns.User. Other fields have been added or removed as
necessary.