Add support for hierarchical taxonomies

Changes the feed manager so it displays categories (or other hierarchical terms) in a tree instead of a flat list:

![screen shot 2014-04-05 at 6 24 45 pm](https://cloud.githubusercontent.com/assets/15995/2623971/a34bf446-bd15-11e3-95bf-cad97cd19207.png)

(oh, and it also fixes the Recently Updated category so that auto-opens on the page load)