Switch to relative imports

The relative imports make it clearer what code is within the project and where
it's coming from.

Just quit it with this relative import stuff.

While I think these relative imports seem to be valid for the running
application, I am having trouble with the django-admin applications
regarding them. I don't see this syntactic sugar as absolutely
essential, so I'm just going to change it now.

Supporters list built dynamically.

Hitherto the supporters list has been committed directly to the static
sponsors/index.html file. This was never ideal and a quick hack to
build Conservancy's supporters list at the beginning of the supporters
program.

With this change, a Django app now exists that dynamically generates the
supporters list.

The database rows must be built from Conservancy's internal Ledger file,
which will be done in a separate script.