Refactored process_sankey() to eliminate 2 redundant variables.
Refactored process_sankey() to eliminate 2 redundant variables.

* uniqueNodes is now a Map.
* Arrays node_order and good_node_lines are gone.
* save_node is split into 2 distinct functions so less inference is needed.
* 'inherit' left/right directives are renamed 'paint'. (That's a better
  word for what happens when Node colors propagate outward.)

No functionality is affected.

nowthis/sankeymatic,nowthis/sankeymatic