Hide rooms that have a defined room type

I have a room with a custom type that's only for holding data, and
doesn't need to be shown in the room list. Currently the spec is a bit
vague about what clients should do, but hiding them is probably fine
for now.

(cherry picked from commit bb9ce117de)

src/models/roomtreemodel.cpp

@@ -286,6 +286,7 @@ QHash<int, QByteArray> RoomTreeModel::roleNames() const
     roles[IconRole] = "icon";
     roles[AttentionRole] = "attention";
     roles[FavouriteRole] = "favourite";
+    roles[RoomTypeRole] = "roomType";
     return roles;
 }
 
@@ -385,6 +386,11 @@ QVariant RoomTreeModel::data(const QModelIndex &index, int role) const
     if (role == FavouriteRole) {
         return room->isFavourite();
     }
+    if (role == RoomTypeRole) {
+        if (room->creation()) {
+            return room->creation()->contentPart<QString>("type"_L1);
+        }
+    }
 
     return {};
 }