Remove url.conf.defaults deprecation warns from Django 1.5 upgrade

Change the names of the url.conf imports to be compatible with Django
1.5 syntax.

Resolves https://github.com/openhatch/oh-mainline/issues/1366

Note that there is still 1 warning in the full test suite that this `url.conf.defaults` is still here, most likely due to 3rd party `vendor/packages/` code but all the OH code no longer references any such `url.conf.defaults`.