GeezerVison

This adds functions to modify shell edges with either a fillet or chamfer but no UI to do so.

The PR is broken into two commits - one that has changes to existing files which could be independent. And one that brings in the new functions in a couple new files.

@ruevs I normally wouldn't want to merge a WIP feature like this, but I think the fillet functionality is at a good stopping point. It lies almost entirely in new files, and you can even build with it without it being called. I'd like to spend some time working on some internals we will need to pass edge selections down to the NURBS code, and it will be easier with this part on master. I understand if you say NO loudly since it's incomplete.

Another reason for this: People have already done this with OCCT, so maybe they would like to try with a built-in capability.

All you need to do to test it is uncomment line 418 in groupmesh.cpp which reads:

       // runningShell.ModifyEdges();

Then go into chamfer.cpp line 296 and change the return value from this function:

double SShell::GetEdgeModifier(SCurve &) {
    return 0.0;
}

Have it return a radius in mm. It will then try to apply that radius to every edge on your shell. This will probably be bad to do with multiple groups, since priors will already have them. The correct way to connect the UI is through that function - it will need to determine which edges a user has selected for rounding and what size. BTW make the return negative to get fillets.

You can try checking coordinates of a curve and only modifying say the top of a text extrusion. But this is in no way a useful modeling tool without a proper UI.

My next steps will be in establishing correct tagging of shell edges with the handle of the entity that created them, or was generated on top of them. That will give us mapping from selectable entities to shell edges. Still not UI, but a step closer.