Feature Request: Calculate Center of Mass

[owenwp]

Ran into this while trying to modify a mesh to add a hanging hook, and the result didn't hang straight. Would also be useful for making bases or designing figurines to balance on their feet. It would be necessary to do this at the gcode level since things like infill and perimeter settings have unintuitive effects.

Could probably get really accurate results by considering the midpoint of each extrusion movement as a point mass.