Creation and deletion of users

As mentioned in https://github.com/OSU-Net/cyder/issues/68
This should be ready to go. All tests pass.
Things to check:
-Adding users to a ctnr
-Adding a user to a ctnr that does not exist
-Removing a user from a ctnr
-Permissions when not superuser
-Admin page perma deleting user
-giving/taking superuser permission
-Creating a user

#TODO switch permissions checking over to backends has_perm