Fixed adding multiple PointLights
Fixed adding multiple PointLights

The pointDistances list was being treated as a JS array, not a proper
List. This should fix issue #137.

brason/three.dart,hirosuke999/three.dart,hirosuke999/three.dart,threeDart/three.dart,brason/three.dart,hirosuke999/three.dart,brason/three.dart,threeDart/three.dart,threeDart/three.dart