Add MassProperties computation for triangle meshes

[sebcrozet]

We should add an automatic computation of triangle-mesh mass properties.
This would implicitly assume that the TriMesh is manifold and have consistent winding.

That paper suggests that this should be fairly easy to implement, based on the existing code that computes ConvexPolyhedron mass properties.

[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).

[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.