The activity window shows recent activity in open worlds.
It can be resized and repositioned. The program remembers the position of the
activity window and restores it to that position next time.
It can be opened automatically at program startup.
It shows: World name, count of recently received lines, total lines received,
world status (open, closed, connecting), time world connected, and duration
world open.
Worlds always appear on the activity window list, so that the same world is
always the same number (and thus you can always use Ctrl+1 to switch to world
1, Ctrl+2 to switch to world 2, and so on).
