title: three.js Plane-Plane intersection point
body: <p>three.js Plane() object has its .intersectLine() method.</p>
  
  <p>I need to retrieve the intersection point of three Planes. A Method called .intersectPlanes(plane_A, plane_B) would be perfect, but is not implemented.</p>
  
  <p>Do you know how to get the intersection point instead?</p>
  
  <p>Thank you!</p>