Only one directional light works at once

[JohnGilbertson]

After getting LightNode to work, I've found that adding directional lights does not work.

If you add one directional light, it overrides the scene's mainLight as generated by lightEstimationMode= LightEstimationMode.AMBIENT_INTENSITY, if you add multiple only the last one added is used.

The simple test is to add multiple directional lights with different colours and see that only the one added last actually illuminates the scene and removes the default illumination.