Cleanup: Separate function for details of the object 'apply' method.
Removed rigidbody build/apply functions from NParticle API. It's better
to keep this functionality inside RigidBody blenkernel for now.
Fix for RigidBodyWorld reading: initialize empty body mempool when
reading blend files, this is not actually stored.
Fix for rigid body removal methods: Flag new rigid bodies for particles
as used to prevent freeing. Also remove bodies if they already exist,
to prevent double adding and subsequent assert failure.
Very basic sync method for particles, which copies the state and
updates the particle positions from rigid bodies.