message: add a 'frist' method to GeometryList to easily retrieve list[0]
diff: @@ -197,6 +197,7 @@ export class PrimitivePolyfaceGeometry extends Geometry {
  export class GeometryList extends Iterable<Geometry> {
  constructor() { super(); }
  + public get first(): Geometry | undefined { return this._list[0]; }
  public get isEmpty(): boolean { return this._list.length === 0; }
  public push(geom: Geometry): number {
  return this._list.push(geom);
  