Bundle stats.js for visualization development

[michaelbromley]

It is helpful when building a visualization to see the frame rate, so one can optimize things.

The current way to do this is to open the dev tools and show the FPS monitor in the "rendering" pane. This works fine, but I would like to make it easier so we can have a keyboard shortcut (e.g. alt + s) to toggle a stats.js fps monitor.