D3v4

[cjhin]

Upgrade to D3v4 to take advantage of more performant physics engine.

Also lots and lots of infrastructure upgrades

TODO:

• [x] sizing
• [x] coloring
  • [x] legend
  • [ ] handle 20+ colors ("other grouping")
• [x] split
  • [x] categorical
  • [x] continuous
  • [x] labels
    • [x] mvp
    • [x] continuous line + filter name
    • [x] fancy physics based from the old version of potato
• [x] resetting filters
• ~~zooming~~
  • [x] instead, implement smart sizing that shrinks to fit
• [x] subselection
• [x] tooltips
  • [x] affordance on hover (make node border pop)

bonus:

• [x] get rid of jquery?
• [x] rewrite in vanilla js
• [x] SPEC TESTS woohoo!
• [x] do d3 the correct way
  • [x] not with a shadow data array
  • [x] not with a shadow animation update loop