Simply implement skipIfCustomUser if not found
Make migrations compatible with user model without `id` field
remove hardcoded auth_user table name from migration 0004
apply Vladimiroff's changes to migration 0004 too (Make migrations compatible with user model without `id` field)
edit migrations so that custom db_table name for user model is respected
closes #35
Merge remote-tracking branch 'jakecr/master'