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.

[ringmaster]

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.

[ringmaster]

First pass

[matt]

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