https://groups.google.com/forum/#!msg/cesium-dev/Bf9MwBgJN8w/5WfUFprBqSgJ

https://stackoverflow.com/questions/34450497/removing-polyline-in-cesium-js  Used

https://groups.google.com/forum/#!msg/cesium-dev/SLGGF3kpp_4/MvLRLVku42AJ

https://developers.google.com/web/fundamentals/primers/promises