Draft: Add volumetric scattering blending model with volumetric shadows
This adds the possibility to blend between VTK's gradient-based shading method and a volumetric scattering model, which uses shadow rays, with a new parameter (replacing the boolean VolumetricShadow). It also adds volumetric anisotropy in vtkVolumeProperty, which is used by the anisotropy model.
Edited by Gaspard Thevenon