Better mass calculation

[Baezon]

PCS2's automatic mass generation is based on the volume of the bounding box, which is a massive overestimate. It should use FSO's calculation when no mass is provided: 4.65 * (bounding box volume) ^ (2/3). This is also wrong and somewhat of an overestimate, but much less bad, and will do for now until a smarter algorithm can be made.