Catalog: separate unread count by board

i.e., separate catalog data. The compound primary
key stuff is pretty nice, though it could use some
querying sugar to match.

>is this the start of an epic new commit streak?!?? :^)
Catalog: count new threads as "updated"

Probably want to change the sorting algorithm
to weight no of new replies by number of current replies;
a huge thread with 10 new replies out of 300 is probably less
interesting than a thread with 5 new replies out of 10.
Catalog: more intelligently sort updated

It looks a bit weird when you actually see the numbers
(why is this thread at the top when this thread has
so many more new replies?). Might need some tweaking
to promote "healthy" threads with 10+ replies over
threads with 1 new reply / 1 total (top of the list
in this sort).