Adding more functions to nppas

[jo-mueller]

Following up on the discussion in this issue, there are a few functions that would be nice to have over here. Among others:

• Smoothing least squares 2D: Can be applied to both surfaces and points so I would suggest the function names smooth_surface_moving_least_squares_2D and smooth_pointcloud_moving_least_squares_2D
• Reconstruct surface from pointcloud: Can be applied to a pointcloud to reconstruct a surface and I think since the removal of open3D functions there is no such function in nppas. Could be called reconstruct_surface_from_pointcloud
• Compute connectivity: Basically connected components labelling on surfaces. Could come handy for object-based measurements (rather than vertex-wise measurements). The results could simply be stored in the value entry of the surface tuple?
• Intersect: A bit more advanced feature, but, interactively intersecting a mesh with, say, a plane to get the line of intersection as a result would be a great way of introspection, especially in the case of more complicated and convoluted surfaces. Other than that, it could be used to do boolean operations with meshes.
• Boolean operations: That being said, boolean operations (adding/subtracting/intersecting meshes) can be helpful to process multiple meshes. Consider the case of multiple segmentations for the same object; The union/intersection could be used on multiple segmentation predictions