added callback functionality to Babelberg
added callback functionality to Babelberg

psieg/babelsberg-js,psieg/babelsberg-js,babelsberg/babelsberg-js,fniephaus/babelsberg-js,babelsberg/babelsberg-js,psieg/babelsberg-js,fniephaus/babelsberg-js,fniephaus/babelsberg-js,babelsberg/babelsberg-js,babelsberg/babelsberg-js,fniephaus/babelsberg-js,psieg/babelsberg-js