Create d3-based node dependency visualization and make CI build it

[scopatz]

Autogenerated and put on website.

[davis68]

Our initial reference was Rosalind. Rosalind seems to use a static SVG-based export from an unspecified software source.

I've looked at the d3js.org gallery and identified some candidate resources for our final visualization:

• https://www.jasondavies.com/collatz-graph/
• http://bl.ocks.org/MoritzStefaner/1377729
• http://www.redotheweb.com/CodeFlower/
• this example cited here as the "Collapsible 2-Way tree" doesn't work in either of my browsers but the thumbnail looks promising.
• https://bl.ocks.org/mbostock/4062045 source page here
• http://taxontree.bpodgursky.com/
• http://www.decembercafe.org/demo/mindmap/ (one of the best)

[davis68]

Will we maintain or generate a master table of node IDs (as part of our CI build) or will this need to recursively find nodes via internal references?