Eliminate base_standard.html template and internalNavigate blocks

The base_standard.html template was an unnecessary level of template
inheritance.

Also removed unused `min` and `subtract` template tags.

Move `SITE_FUNDGOAL` configuration to settings/base.py

This changes more often than the surrounding code, so should live with the other
configuration.

Merge sponsors.py into supporters app, frontpage.py into views.py

Just a small structural change so that the related functionality is grouped together.

Remove remaining jQuery

This avoids every page on the site parsing 250KB of JavaScript.

supporter-page.js isn't the most elegant code, but at least it's a little more
modular now and no longer user jQuery.

Delegate management of canonical URLs to Apache

This middleware is mostly redundant:

* redirecting to canonical URLs can be done more simply in Apache
* appending a forward slash is a default in CommonMiddleware now
* we're no longer using Squid cache

May need to update Apache to strip/redirect trailing "index.html".

Switch settings to use "the one true way" approach

The advantage of this approach is that the production and dev configurations are
in version control, so there's less opportunity for surprises.

As advocated by Jacob Kaplan-Moss (OSCON 2011) and Two Scoops of Django book.

Add to-do file

This allows me to track improvements we'd like to make, but not necessarily
straight away.