Style update.php

This patch makes update.php look an order of magnitude better and the HTML actually validates. The inside of the pages stays the same, patches to do the real UI work will be coming one page at a time.

The one content change is the "All" option for updates is removed because no one in their right mind should ever run every update since June 2002 and people who are new to updating Drupal might mistake "All" for something that they want.