Add an 'all' argument to drilldown_tree_for_node

This adds a new optional argument (immediately after the required arguments) to have the function return all descendants of the node, not just its immediate children.

I added this because I wanted the cumulative count functionality of drilldown_tree_for_node, but wanted to show all the descendants of a particular node, not just its children. I'm not sure if there's a different/better way I could have done this, feel free to let me know :)