Read doubleSided from GLTF material

Author: einarf

demosys/scene/loaders/gltf.py

@@ -601,6 +601,7 @@ def is_resource_node(self):
 class GLTFMaterial:
     def __init__(self, data):
         self.name = data.get('name')
+        self.doubleSided = data.get('doubleSided') or False
 
         pbr = data['pbrMetallicRoughness']
         self.baseColorFactor = pbr.get('baseColorFactor')