D3 v4 forcelayout example with dropdown filters.
forked from mbostock's block: Force Dragging I
forked from almsuarez's block: Force Layout v4 with Filters
forked from almsuarez's block: Force Layout v4 with Filters v2
forked from almsuarez's block: (d3v4) Force Layout w highlights
forked from almsuarez's block: (d3v4) Force Layout w complex nodes