title: Three.js Trackball Controls limit rotation and pan
body: <p>I have a plane that the camera is looking straight at and am using Trackball Controls to be able to zoom, pan, and rotate the plane. I realize that currently there isn't a way to limit the rotation or pan like can with zoom in the file, but was hoping there is a fix for this.</p>
  
  <p>I'd like to limit the rotation to only a few degrees and not be able to flip the plane in anyway. Also, I'd like to only allow panning when the plane is still visible on the screen. I don't want to allow a user to pan and be able to remove the plane from the window. Is there a quick fix to add to the Trackball Controls or how do I go about setting limits to the rotation and pan? Or is there a better type of control for handling this functionality?</p>