Visualization of normals

For debugging purposes:

You can replace the L_out = Spectrum(5.f ...) in pathtracer.cpp that the starter code gives you with:

  (isect.n).normalize();
  return Spectrum(isect.n.x/2.0 + 0.5, isect.n.y/2.0 + 0.5, isect.n.z/2.0 + 0.5);

Reference results for CBspheres, bunny, dragon, and wall-e: