3D: smooth an object along a smoothed z-trace #125

Problem

There is no way to smooth a 3D object along a smoothed z-trace, which Legacy supported. This is a larger feature, carded here for visibility.

Proposed

Smooth an object's mesh along a smoothed z-trace, matching Legacy parity. Scope and approach to be worked out; this issue tracks the request.

Part of #66.

Source: PyReconstruct Wishlist, 3D scene, "Object Alignment smoothing in 3D scene".

Once you have a good smoothed z-trace, it would then be good to smooth the 3D of the object itself by that smoothed trace (as in Legacy Reconstruct).