Rework ActionsHandler as static helper functions.
The functions are now invoked from ChatBarCache so there is no need to pass an actions handler object around qml simplifying the code.
So at the moment this remains behind the feature flag as this only adds a threadmodel and a basic visualisation. There is much more to come to get it ready for full release.
Depends on https://github.com/quotient-im/libQuotient/pull/695
Currently basic just to show a working implementation using RoomMember. Currently only the room event and search models are moved over. Will change everything else over once the dependent pr is complete.
