We were so smitten by the spectacular black-and-white bead-encrusted art-deco dress Florence Welch wore for her first number, “Shake It Out,” on this weekend’s Saturday Night Live that we couldn’t pay attention to the song at all. We kept trying to will her to turn around so we could see the back and for the camera operator to settle on a full-length shot for a moment. Seriously, did you see it? Any info?