make webgl version of voronoi plot with improved interactivity

[cornhundred]

WebGL should be able to handle ~100,000 cells as voronoi plots (~10 triangles per region). This will give us the speed to zoom and change colors more quickly

We should also add two-way communication (e.g. to heatmap).

We need to be able to select regions of cells from the image and show them on the heatmap.

We need to load a pre-clustered heatmap - clustering ~100,000 cells every time the dashboard starts will be too slow. For now we can load the pre-clustered visualization JSON.