Improve selection of points to compute planes on each surface

[rdrighetto]

Instead of iteratively finding which points are above/below the current plane, calculate only central plane and select top % points further away (say the 95th percentile) from this plane. Might make estimates more stable and accurate.

[rdrighetto]

This is proving more challenging than I expected...
Some current attempts at
https://github.com/CellArchLab/slabify-et/tree/points_selection (improving selection of points based on distance stats)
and
https://github.com/CellArchLab/slabify-et/tree/stop_criterion (keeping the current iterative approach but trying to define an automatic stop criterion)
Any help is appreciated 🙂