 √ Fix snap to grid. Final nudge missing.
 √ Add menu item for different selection modes.
 √ When we have to scroll, some items draw several times. Why?
 √ Make view resize again when an item is dragged outside its bounds while
	sizeToFit=YES
 - When no empty selection and no multiple selection are on, multiple still
	works with shift.
 - Multi-item drags can occasionally cause items to end up off-grid?
	Or was it off-grid to begin with?
 - When an item is dragged out the upper left, shouldn't we re-scroll? We should
   retain the visible items by reversing the scroll, though.
 - Keyboard navigation is broken for items scrolled out of view when looking
	them up through the cache.