fixes #398

fixes #393

fixes #394

fixes #249

This was causing some flickering when many messages were added.
Mostly visible on macOS.

fixes #357
fixes #335
fixes #230

The old algorithm during filtering will check every room
if it's part of the group. O(N*G)

The room ids for a group are now stored in a map for faster lookup
so the search can be completed in a single pass. O(N)

That's a fix to deal with long running sessions which will end
up taking more & more memory given enough time.

fixes #378