An exhibition that recently opened at the Neue Galerie, “Neue Sachlichkeit/New Objectivity,” has a sister show in Germany at Kunsthalle Mannheim, “The New Objectivity; A Centennial.” As the title of the Mannheim exhibition intimates, it’s been a hundred years since a historian, critic, and curator, Gustav F. Hartlaub, mounted an overview on its premises of a cadre of contemporary artists who practiced “a new naturalism.”