Changed from div to using svg.

That was probably a bad idea, for two reasons:

1. Not sure what React does. The element is updated (according to the "Prop" window in the React devtools), but accoring to the same window, in the list, it isn't updated. No idea why.

2. Doesn't solve my main problem: Too many DOM elements for the browser to handle performantly.

Next try: Canvas! (Even though this will kind of make Om/React useless in this project...)
Change from SVG to canvas.

It seems to work, so that makes me happy.