title: How to clone an object3d in Three.js?
body: <p>I want to clone a model loaded with loader, I found <a href="https://github.com/mrdoob/three.js/issues/1363" rel="noreferrer">this issue</a> on github,but the solution doesn't work. It seems there has been an structural change in Object3D.</p>
  
  <p>How can I clone an Object3D in current stable version of Three.js?</p>