Updated images

Following an email discussion with @katychuang, here's a shot at updating the photos on the Compose website.  These are Creative Commons Attribution 2.0-licensed photos by Steven Pisano, from his collection "New York Street Scenes 2014" at https://www.flickr.com/photos/stevenpisano/sets/72157645579250535/ .  Let me know if this works!

The goal here is to avoid using photos of people who haven't attended or endorsed Compose, and who didn't necessarily agree to having their photos used to advertise for it.

Thanks!