Consolidated fixes

Issues / Pull requests included:
* Django 1.5 Custom User Model support. (Pull requests #138, #133, #130)
* Stop bad data from breaking activity stream (#140)
* fix south migration warnings (#139)
* Load url tag from future (#137)
* Avoid deprecation warning (django 1.5) (#136)
* Added south migrations fix for issue when migrating a fresh project that uses Custom User Models. Done similar to [this](https://github.com/lukaszb/django-guardian/pull/116/files)