Claribel and Etta Cone, two sisters from a prosperous Jewish family in Baltimore, began buying works by Matisse, Picasso and other members of the avant-garde back in 1905, when critics were still disparaging Modern art. By the time the Cones’ collection was bequeathed to the Baltimore Museum of Art in 1949, they had amassed some 3,000 objects. The selection here is a celebration of their taste.