Refactored user creation and update via REST API. Used new serializer.
Cleaned up management commands, signals and imports. Moved code from 'api.py' to 'models.py'.
Changed usage of group 'Registered'. Now the users don't have to be members to gain its permissions. Used customized auth backend for this.
Added and changed some tests.
Added api for groups.
Refactored serializers now using 'id' instead of 'url'.
Rework of tornado autoupdate functionality.
Implemented extra data in SockJS messages.
