OIDN denoiser, volume plots

• Included Intel Open Image Denoiser: HDR/LDR, supporting RGB/Albedo/Normal inputs.
• Switched to optional counting of transmission path segments (previously they were counted always and included in
  the segment range limits).
• Const-size geometry primitives (same radii, or u/v/w vectors for all data points) with much lower memory
  consumption, beneficial e.g. for volume plots.
• Volume coloring material for semi-transparent volume visualization (experimental).