Directly before entering a newly opened show at NYU’s Grey Art Museum, “Make Way for Berthe Weill: Art Dealer of the Parisian Avant-Garde,” viewers encounter a small picture of a big personality, a 1933 portrait of the exhibition’s namesake by a Czech artist, George Kars. Surrounded by an abundance of casually stacked canvases, Weill is depicted as bug-eyed and stolid, her black raiment and erect carriage connoting immovability as much as eccentricity.