Copy volume attributes to snapshot textures

The textures now have the brightness, threshold, and other attributes from the IGTLink volume, however it will not show on the actual snapshot model.

As far as I can tell, there isn't a way to apply those attributes to the model texture without modifying the image data itself, since the model only references the image data for its texture. I could probably throw together a way to approximate the way you can change the look just like in the slice viewer, but it would require adding quite a bit and Simon (who original requested the feature) only uses the texture nodes anyways.