Based on D3 Stacked Bar Chart by Mike Bostock https://bl.ocks.org/mbostock/3886208
Tooltip code based on D3 Stacked Bar Chart with Tooltips by Michael Stanaland /mstanaland/6100713
forked from mjfoster83's block: D3js v4 Stacked Bar Chart - with Tooltip Hover
https://d3js.org/d3.v4.min.js