Removed ununsed import, and did other cleanups

apps/permissions/models.py

@@ -2,7 +2,7 @@ from django.db import models
 from django.utils.translation import ugettext_lazy as _
 from django.contrib.contenttypes.models import ContentType
 from django.contrib.contenttypes import generic
-from django.contrib.auth.models import User, Group
+from django.contrib.auth.models import User
 
 
 class PermissionManager(models.Manager):