Make use of new RoomMember item from libquotient

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.

src/roommanager.cpp

@@ -256,7 +256,6 @@ void RoomManager::openRoomForActiveConnection()
 UriResolveResult RoomManager::visitUser(User *user, const QString &action)
 {
     if (action == "mention"_ls || action.isEmpty()) {
-        // send it has QVariantMap because the properties in the
         user->load();
         Q_EMIT showUserDetail(user);
     } else if (action == "_interactive"_ls) {