Upgrade ruby, rails, and CMS

I had to make a lot of changes to deal with the CMS upgrade I'm
afraid.  Also removed some spurious/unwanted/breaking tests that Rails
had helpfully autogenerated for us.
Take a different approach for loading CMS.

Fixtures don't quite do what we want (they don't let the site admin edit
the pages) so we should load default stuff a different way.
Load CMS skeleton (site/layout/topnav)
Load CMS snippets from files
Added snippets for the whole homepage and "add site" form

Also changed "community garden" to "food garden" throughout.
Modified tests to take snippetified content into account

... since we can't rely on a page necessarily having the content we
expect any more.
Removed partials that aren't needed any more
s/community garden/food garden/g