Did you know there’s a hierarchy in art mediums? Painting has long reigned supreme, the most coveted, the most expensive. Then comes sculpture, then works on paper. Further down: installation and video. And at the very bottom? Photography. Wild, right? For decades, photography was seen as journalism, not art. The Whitney didn’t even start collecting it until 1991. Which is why Mix and Match — the new Nicola Erni Collection book — feels so exciting. It celebrates her 6,000-strong collection, feat