RigidBody/Joint/etc. Cloning

[SneezingCactus]

Currently, cloning physics objects like RigidBodies is really inconvenient and potentially slow, as you have to manually recreate the descs (unless you store every desc you use for the creation of the RigidBody, that is, the RigidBodyDesc and each one of the colliders' descs).

It'd be nice for there to be an integrated RigidBody.clone()function for this behaviour, or perhaps a better way to build a desc from a physics object.