title: PyQtGraph - Turn off perspective in 3d view
body: <p>I'm using PyQtGraph to plot mesh surfaces. I would like to see the 3D world with perspective turned off. </p>
  
  <p>Is this possible in pyQtGraph? I have searched through the documentation and the google groups and can't find any reference to this. I think it is possible in principle with openGL so is there a way to bring this out and control perspective on/off in pyQtGraph?</p>