Refactored SiteMap to be generic
With this mechanism (in combination with the new sidebar) in place
adding a new entity to the site becomes very easy, rather than having
to add a lot of code to 'map.py', one can simply register with
the sitemap modules.
from django.dispatch import Signal
request_started = Signal()
request_finished = Signal()
got_request_exception = Signal(providing_args=["request"])