Pass treepath to node to range map

In general using the treepath is more natural here. While the node stores its treepath this is very likely to be removed soon, since in any place where you need the treepath it's available by other means (e.g. during tree traversal).

Notice that this is an interface change! If you have implemented your own node-to-range map, you will have to add the additional parameter to operator().

At a later stage one may also want to drop the node argument. However, it's not totally clear if this is needed in custom maps.