(other structures which have a facet as key-value are converted to vectors)
Using const Polyhedron& as a parameter (previously I was using Polyhedron pointer).
mesh_segmentation.h added for API which includes free functions.
AABB_const_polyhedron_triangle_primitive.h is added for supporting Facet_const_iterator as a parameter to AABB Tree. (I am not sure that is the best solution.)