Make JSON material configs xeogl.PhongMaterial by default

[xeolabs]

    new xeogl.Entity({
        //...
        material: { // <<--- Should default to xeogl.PhongMaterial
            diffuse: [0.3, 1, 0.3],
            emissive: [0.4, 1, 0.4],
            lineWidth: 6
        }
    });