Add light map to materials imported from Collada

enumerateChildNodesUsingBlock.swift

sceneView.scene!.rootNode.enumerateChildNodesUsingBlock (){
            node, stop in
            if let materials = node.geometry?.materials {
                for material in materials {
                    //Blender export doesn't support multiple textures per object, so we add our lightmap to the 2nd UV channel here
                    let image = SCNImage(named:"WorldLightmap")
                    material.multiply.contents = image
                    material.multiply.intensity = 0.7
                    material.multiply.mappingChannel = 1
                }
            }
        }