Indicate and sort on rooms with unread messages

[ulyssa]

This fixes #83 by adding two new fields to sort on, unread and recent. I've updated the sort order for "rooms" (and therefore by default all of the other room-like lists) to now be ["favorite", "lowpriority", "unread", "name"], so that favorites will still be at the top, and low-priority items at the bottom of the list, with unreads at the top inside those groups, and finally sorted by names.

The "recent" sort field can be used by folks who also want rooms to move within the list based on how recently someone has messaged there. This could potentially be annoying for users in multiple rooms with frequent activity that keep swapping positions in the list, so I haven't put it in the default sort.