Changed MARGIN back to 2 pixels since the retina display issue appears to be fixed.
Improve look of menu options, particularly for disappear interactions. The disappearing object (apple) will be grouped to the receiver (horse). The image of the subject performing a transfer and disappear interaction (farmer) will be horizontally flipped and moved closer to the disappearing object to make it look like it is giving the object to the receiver. Additionally, if an object is already grouped to other objects, the menu options should show most of these (e.g. when the farmer puts hay into the cart, the menu option should show farmer, hay, cart, AND tractor).
Check if steps exist before accessing solution in pan gesture. This should allow objects to be moved even if no metadata file is included in the epub.
Fixed bug where app would crash trying to create a menu item image for an object that does not exist on the page. This happened because the currentGroupings array was not re-initialized each time the page loaded (via pressing the Next button).
Code cleanup and adding additional comments
Changed MARGIN back to 13. It seems that retina displays need a larger margin value. We should calculate this based on the display later.