Adds podcasts and refactors the current set of feeds.

1. Integration points: A new item to the footer that shows feeds, a new RSS icon on all search results pages.
2. New podcasts created for every jurisdiction, and for oa search results.
3. Removes the feeds app, and refactors the code from there into several feeds.py files, which are crammed into various apps.
4. Fixes issue with inaccurate audio length estimations by switching to a constant bitrate. This allows us to put the duration in search results, and I've done that as well.