Give a radius option

[Andreya-Autumn]

Making resize actually resize is probably step one. But from experience, the current resize behavior (which just extends the viewport on the infinite lattice) is also useful for some things.

So eventually, offer a way to set the spheres radius inside the resized window. So you can make a bigger window that shows many smaller spheres (useful on huge screens) or a bigger window that draws the spheres bigger (more easily readable). Etc