Restore setup option
Add MANIFEST.in to control package data

Previously, we were using some hacks copied from old Django setup files
to get the templates to be included. However, this broke somewhere
around python 2.7.

Instead, use the simpler more conventional MANIFEST.in with a
recursive-include for all py, html and txt in the package.
Switch back to templates specified in setup

MANIFEST.in causes files to be included in the sdist, but not to be
installed when installing using pip.  Switch back to listing files in
setup.py.  Rely on "zip_safe=False" instead of purelib, and try
simplifying the listing of files.