DnD: Fix issue when dragging previously-dragged row to end of grid
DnD: Prevent error in short-circuit logic on long drags

This specifically involves cases where an item is dragged a long enough
distance such that the original row is destroyed.
DnD: Cleanup

I'm a horrible person.
Merge branch 'master' into dev-0.4

Conflicts:
	extensions/DnD.js