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.