-voronoi_utility.py:
	-wrote new method Voronoi_vertices_spherical_surface() for calculating the Voronoi vertices based on the sphere surface Delaunay triangulation (may not be perfect yet)
-voronoi_utility.py:
	-started working on new method (Voronoi_polygons_spherical_surface) to identify the polygons in the spherical Voronoi diagram and generate a convenient data structure for handling them
	-refactored code a bit to prevent duplication / facilitate maintenance