Add various things that are needed for GThree

I ported gthree to the new geometry types, and some things were missing.

Also, i think graphene_sphere_init_from_points() and graphene_box_init_from_points() are kind of weird in that they take an array of pointers-to-point3d. I made init_from_vector take an array of actual vectors, and i think from_points should to, but I didn't change that.