[STAPLE/geometry] add generic use functions

[modenaxe]

For example:

• [ ] identifySphericalArticSurf.m: a function that slices along a predefined axis and keeps storing the profiles. Then checks the reconstructed surfaces (before they join) and with curvature analysis can fit a sphere, whereever the bone comes from.
• [ ] fitAnalyticalShapeToArticSurf: again using curvature analysis, articular surfaces could be identified, e.g. planar surfaces (clavicula, tibial plateau, talocrural mortise, etc)