docs: public void makeTouchable(GVRSceneObject sceneObject, OnTouch handler) {
          if (handler != null) {
              if (sceneObject.getRenderData() != null) {
                  if (!touchHandlers.containsKey(sceneObject)) {
                      makePickable(sceneObject);
                      touchHandlers.put(sceneObject, new WeakReference<>(handler));
                  }
              } else if (sceneObject.getChildrenCount() > 0) {
                  for (GVRSceneObject child : sceneObject.getChildren()) {
                      makeTouchable(child, handler);
                  }
              }
          }
      }