podjango: Link up "The Corresponding Source" title

This helps with navigating back to the home page.

Merge podjango.apps.cast into main podjango module

It's much simpler if "podjango" is the name of the Django app with a single
urls.py etc. The reason this is required is because podjango was originally a
fully-blown Django website and now it's become a Django app within the
Conservancy website.

Rename cast to "The Corresponding Source", move to URL prefix "/cast/"

Also improved detail view rendering where unclosed <ul> tags in the body
content HTML from the database were affecting the display of footer info.

Merge FAIF "podjango" codebase into main sfconservancy.org site

It's a little awkward for now with podjango also having an "apps" module, but we
can clean that up later. I've excluded any JS and HTML that's likely not
required.

To accomodate this merging, I moved the templates into a "podjango" subdirectory
and, added a "podjango" namespace to the URLconf and converted a bunch of
hard-coded links to use the "url" template tag since there will now be a
"/faif/" prefix.