SpecialWantedcategories: Show more current information when in cached mode

Usability improvements I thought up when trying to through nearly
500 entries on this page on pl.wp.

* Strike items on the list if the category was created or emptied
  since the last update
* Show current number of items if it's different from the original one

Change-Id: Ifcc534f19fb60732bcd40f75ddca390106ebe28e