No layout performed on move of rest up/down
Add staff text or lyric or other marking to a rest. Now use arrows keys to raise/lower the rest toward the marking. No attempt is made to avoid collision, until you stop moving the rest and then do some other operation that forces a layout of that measure. That is because we don't actually call setLayout() when changing offset for rests, unless there is a beam present. I can't think of a good reason for this, so I'm fixing it.