Add lazy image loading and display images in rows
Images were displayed out-of-order and tried to load all at once, which
was bad for users with large query results. Now images load lazily but
preload well beyond the window. Images load in parallel and are all of
uniform height within each row so the bottom isn't staggard. I had
created a version where images remained queued to be loaded even after a
new query was begun; that is now fixed.