PEP8 cleanup, unused imports, missing imports, style cleanups

mayan/apps/permissions/migrations/0003_clear_permission_holders.py

@@ -1,20 +1,18 @@
 # encoding: utf-8
-import datetime
 from south.db import db
 from south.v2 import DataMigration
 from django.db import models
 
+
 class Migration(DataMigration):
 
     def forwards(self, orm):
         for permission_holder in orm.PermissionHolder.objects.all():
             permission_holder.delete()
 
-
     def backwards(self, orm):
         raise RuntimeError("Cannot reverse this migration.")
 
-
     models = {
         'contenttypes.contenttype': {
             'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},