Update material.py for blender 3.3.0

[jtsage]

The name of the "Separate RGB" input has changed from Image to Color in blender 3.3.0. Also support just using an image named "Glossmap" instead.

This change is protected by a blender version check.

The "old way" that still works - using the newly renamed node "Separate Color", manually re-named to "Glossmap"

An optional "new way" - using just an Image Texture manually re-named to "Glossmap"

I've not delved deeply into 3.3 yet, but other than this, it all seems to be working correctly - only re-ran a couple quick exports to see if they appeared the same. Fwiw, been on 3.2 for a week or two prior to this, no issues found there.