Update Dashboard via cron

[ringmaster]

Loading the dashboard can be slow due to fetching of the feeds required for its display. Fetching those feeds during a cron operation should improve response times.

Feeds are cached for half a day. A new schedule for Twice Daily should fetch the feed at appropriate times.

The fetch_rss() calls in wp-admin/index.php should remain because they fetch the feed from the magpie cache and if the cron fails for some reason, it will still work.

There must be a better was to set up default crons. Please feel free to move or augment what I've got to somewhere that makes more sense.

First pass

This isn't needed anymore because of the AJAX loading on the dashboard, it makes it quite fast.