Seven valuable art pieces plundered by the Nazis more than 80 years ago are being returned to the heirs of a cabaret performer, who was killed during the Holocaust and whose massive art collection was stolen by the Third Reich. The descendants of Fritz Grünbaum have been seeking the return of more than 400 pieces of art, including 80 sketches by the Austrian expressionist Egon Schiele. The artwork is worth many millions of dollars, although the whereabouts of many of the pieces remain unkno