Move reply pane to use MessageContentModel. This means the reply pane component is no longer required.
This commit also limits the size of code and image componets in a reply to keep them from getting too huge.
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.
