Just when you thought there was nothing left to explore in Picasso’s oeuvre, here comes “Picasso: Black and White” offering a whole new way of looking at this artist’s seemingly unfathomable achievement. Here, striped down to bare essentials of light and shade, Picasso may be at his best. Curated by the Guggenheim’s Carmen Giménez, with an extraordinary amount of cooperation from Picasso’s heirs, the show contains numerous works never before shown in the U.S.