Fixed imports for django 1.6.

Works from django 1.4.
See https://docs.djangoproject.com/en/1.4/releases/1.4/#django-conf-urls-defaults
Fixed urllib import errors for python 3
Added SSO_SYNC_USER_KEYS setting
Updated changelog
Copied 'local django settings import' comment from elsewhere in the file
Merge pull request #5 from lizardsystem/reinout-django16-python3

Python 3 and django 1.6 support and new SSO_SYNC_USER_KEYS setting