Replace HomeSettings with Presence Model class. Replace SiteSettings with
Site Model class. Derive Group Model class from Presence, adding the "home
page settings" properties in a Melange site presence to every Group.
Patch by: Todd Larsen
"""Multi-consumer multi-producer dispatching mechanism
Originally based on pydispatch (BSD) http://pypi.python.org/pypi/PyDispatcher/2.0.1
See license.txt for original license.
Heavily modified for Django's purposes.
"""
from django.dispatch.dispatcher import Signal