Made URL application namespaces be set in the included URLconf and
instance namespaces in the call to include(). Deprecated other ways
to set application and instance namespaces.

Thanks Carl Meyer for the suggestion and Alex Gaynor and Carl for reviews.

* Removed ADMIN_FOR setting and warn warning
* Group view functions by namespace instead of site
* Added a test verifying namespaces are listed

Thanks to Claude Paroz for reviewing and ideas for improvement.

Thanks Bouke Haarsma for the review.

Don't set a global default interpreted role function for reStructuredText.
Instead, use the `default-role` directive to change the default only within
the `parse_rst()` function.

Thanks Malcolm Tredinnick for the report.

Should be unneeded with Python 2.7 and up.
Added some unicode_literals along the way.