Progress on #10: Man this is basically working!! :)

Somewhat laggy, esp. in Firefox and Safari, but... hopefully fast
enough? Maybe I can speed things up a bit with some more indexing,
since I imagine _.find is slow.

Notably, there's a big ol' bug with the upper three [0%, 50%] pools
incorrectly using the [0%, 25%] yScale due to the variable yScale
thing, highlighting that I did it poorly in the first place.