NEW YORK – Picasso studies, and exhibitions, seem increasingly like shale oil extraction: It takes ever-greater investment and resources to extract a diminishing supply of desired product. “Picasso in Fontainebleau,” a midsize show at the Museum of Modern Art, digs deeply into just a few months of production, the summer of 1921, when the artists worked in a rented house in a town some 40 miles outside of Paris.