display artists, album years (including 0 years)
add d3 as sourced from http://d3js.org/d3.v3.js just now
display albums by year in heat-mappy style
break vis into albums/singles/compilations
add Promises polyfill

from http://s3.amazonaws.com/es6-promises/promise-0.1.1.min.js
origin https://github.com/jakearchibald/es6-promise
checkpoint limited tracks vis support

experiencing weird polymer/d3 interaction problems wehre the track
visualizations are all somehow ending up in the same DOM node, I think because
of shadow DOM and/or templating interacting in a bad way with d3.
improve scrolling glitches; track-vis still broken