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)

The latter will not always return a valid pointer.

fixes #363

- Run the linter
- Explicitly use cmake for installing olm

- Patch the olm repo with a CMakeLists.txt file

fixes #204
fixes #255