Dragging item(s) within the same window while holding the Apple key down should make a duplicate

[ph0enix-c0der]

As referenced in issue #228, dragging item(s) within the same window while holding the Apple key down should make a duplicate of it or them, just like Mac OS 8.0 and later on the Mac.

[inexorabletash]

This is doable for single items. Desktop does not (and will not) support Duplicate for multiple items.