Calculate a max value for the "Edge Thickness" slider #60
Description
The natural choice is having spheres (or horospheres, geodesic planes) barely touch at the max value.
As part of this, I've wondered if we want to allow negative edge thickness, but I'm not sure how to make the UI good for that. It's nice that you can move the slider all the way to left to get zero thickness. So maybe we don't worry about it.