unfold surfaces

[r03ert0]

Implement input of 3d surfaces to be unfolded along with fibres.
Surface format should be PLY, which is fairly standard, supported by Blender, meshgeometry, among others.
In the current implementation (which is DTI only), each fibre is processed one by one. Each vertex of the surface is transformed with the selected algorithm and the output saved as a .fib file. For surfaces, each vertex should be transformed independently, and the result saved as a PLY surface.