Upgrade JavaScript libraries

Resolves #34 by upgrading jQuery, jQuery UI, Backbone, Underscore and json2 to their latest stable versions.

To resolve some issues with jQuery UI I had to recreate the theme using their ThemeRoller service, but I think I got a pretty good match.

Only minimal changes were needed to code-comments.js to accommodate the upgrades.

Tested with the following browsers on Ubuntu 14.04 LTS:

* Google Chrome 37.0.2062.20 beta
* Firefox 31.0