Make format tables sortable

This uses [sorttable.js](http://www.kryogenix.org/code/browser/sorttable/) to enable sortable table headers for a few of the big format tables, most notably the Supported Formats table. It also converts the ratings columns of that table to be more compact using images, like it was on the previous LOCI-based version of the site (so those columns are sortable as well).

Big thanks to @sbesson for the initial work on integrating sorttable support into the Plone theme.