RSS widget done

So, the RSS widget is up and displaying on the front page. I'm rethinking the caching scheme, though, so it works like this:

When we go to display a feed, we call cache_feed on it. This gives us the feed back, in addition to re-fetching it if it's stale (we'll define stale to be say, older than 10 minutes). We'll also rig it up so that there are no feeds showing off the bat, and they only get loaded if someone tries to look at them (and thus only get recached if someone tries to look at them). This should cut down on overall server load.

refresh_cache got renamed to clean_cache, and it deletes feeds that aren't being subscribed to. It also nixes all the items off of feeds that are stale anyway. This should get called maybe once an hour in a cron job?