Add MassProperties computation for triangle meshes about parry

[sebcrozet]

@metric-space Yes, it’s implemented now, this issue can be closed.
@wlinna There is no automatic calculation of the mass properties when the mesh is built. It needs to be calculated by calling trimesh.mass_properties() explicitly.

[metric-space]

@sebcrozet would it be fair to say you've already implemented this?

[wlinna]

I use parry for processing arbitrary (i.e. I can't change the input itself) BIM models, and there's no guarantee that each mesh in a model will be manifold or have consistent winding. I hope these "automatic computations" will stay opt-in, i.e. only computed when set_flags is called with specific flag(s).