This also removes an ugly hack, that was needed before.

When user is mentioned (via matrix 'highlight_count'), inactive
rooms will use a different color for the notification circle than
when only general unread messages exist.

fixes #313

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)

- Patch the olm repo with a CMakeLists.txt file

fixes #291

fixes #253

This can happen when a new room is being created from a different client and thus is created
with no known state to the local client.