continuous intersection testing (and magnetic snap-to)

[roambotics_scott]

Very often in assemblies it's important that parts fit together and not overlap.

It'd be great if there were a way to have interference (ideally with the ability to specify positive or negative tolerances) automatically checked while we're designing.

I'd love it even more if whenever we're doing something like pulling a face, we could just snap that face to other bodies to bring them just into a specified tolerance (again positive or negative to allow for free or guided motion and interference fits).