Position of backsides on backsides preserved
Backsides on backsides recreated

Fixes a bug where JQuery UI button isn't called.
Color of backsides is preserved

Including the top-level backside. Can edit backside color and it is
reconstructed properly.
Drop of top-level backside drops contents

Too confusing and too hard to handled multiple top-level backsides so
dragging one drags all its contents instead.