title: Create and use a target for SCNCamera
body: <p>I come from 3D software use, wherein most cameras have a target, which makes moving the camera and its view point much easier, generally speaking, then using a "free camera" that's not got a target.</p>
  
  <p>How would this be done in Scene Kit? </p>
  
  <p>e.g. my first thought was to use an SCNNode as a dummy sort of target, fixed in the world space, connected via a physics joint to the camera. </p>
  
  <p>When wanting to pan the camera, release the dummy from its lock in world space. All other operations (rotate, dolly, roll) the camera moves around/to the fixed dummy. And moving the dummy causes the camera to track it.</p>
  
  <p>Is there a better way? Or easier way? Or more sensible way?</p>