message: Don't require transform matrix and material file
  lights.json doesn't have these..
diff: @@ -659,13 +659,18 @@ void load_moana(std::vector<std::string> const& filenames, model& mod)
  // matFile
  + if (doc.HasMember("matFile"))
  + {
  std::string mat_file = doc["matFile"].GetString();
  load_material_file(island_base_path, mat_file, materials);
  + }
  auto base_transform = std::make_shared<sg::transform>();
  root->add_child(base_transform);
  // transformMatrix
  + if (doc.HasMember("transformMatrix"))
  + {
  int i = 0;
  rapidjson::Value const& tm = doc["transformMatrix"];
  if (tm.IsArray())
  @@ -676,6 +681,7 @@ void load_moana(std::vector<std::string> const& filenames, model& mod)
  assert(i <= 16);
  }
  }
  + }
  // geomObjFile
  