First pass at remove and a visit that includes parents.
- Modified d3_geom_quadtreeNode to create node with parents.
- Updated remove() to use node.parent instead of expecting to get it throw d3_geom_quadtreeVisit.
- Added d3_geom_removeNodeFromParent and d3_geom_pruneNode for remove() to use to remove a node once its found and to prune the node from which it was removed.
- Updated remove test to make sure the tree is empty once everything's been removed from it.