Space samples and reheat buttons do not work with draw_node()

[kitchensjn]

Don't know how this slipped through the cracks, but makes sense as draw_node() doesn't differentiate terminal nodes so doesn't know how to evenly position these. This leads to similar problems as #79, so may be worth tackling sooner rather than later.

[kitchensjn]

Similarly, there is a lot of bloat in the JSON because evenly_distributed_positions is calculated based on the big ARG, so even if you are only plotting a small subgraph you get a giant array of numbers. This should be instead calculated based on the number of terminal nodes or something similar.