message: add common `visible` param to all lights
  add light type as child
diff: @@ -22,8 +22,10 @@ namespace ospray::sg {
  {
  auto handle = ospNewLight(type.c_str());
  setHandle(handle);
  + createChild("visible", "bool", true);
  createChild("intensity", "float", 1.f);
  createChild("color", "vec3f", vec3f(1.f));
  + createChild("type", "string", type);
  }
  NodeType Light::type() const
  