added indices and cleaned up notification

re actor_id, we do have those lookups... in WQL!  (the edited_by queries we just fixed).  They're not the most common queries, but they are on the menu of cards with accounts (account > edited) and they feature prominently on some sites (including on Wikirate profile pages), so I think the index is probably worth it.

re multiple-columns: I get that these are common combinations, but there's some overhead in indeces, right?  I suspect at some point we may want to test to make sure it actually speeds things up.  If this does work, I guess it's likely that we want "key and trash" index on cards at some point, too.

ultimately this is not terribly difficult stuff to test, so we can be data-driven here.