A bunch of updates and fixes

I've done a bunch of stuff in my branch:

- Rejiggered the commit history to be based on the SVN trunk (both to get the old commit history, and to get some bugfixes which hadn't been in the last release tarball)
- Disabled the column view and image hover stuff, which wasn't behaving very well and impacted readability negatively
- Added a share-to-Twitter plugin
- Added some intelligence into the update logic that makes it only update feeds at a rate based on how frequently and regularly they update (rather than pulling everything at the same rate); this makes a huge difference when you have several hundred feeds of which many only update once a week and a few haven't updated in a year or more. :)