shiftLayout after dragComplete (instead of layout)

**Test case:** http://codepen.io/desandro/pen/QyrEgX

Is it possible to have packery with dragabilly do shiftlayout instead of a complete layout ?

Start with the reduced CodePen test case linked in the issue and inspect how Packery is used with Dragabilly during drag completion. Confirm the current complete-layout behavior, then determine whether the requested result is a shiftLayout after dragComplete; done means the example demonstrates that behavior without breaking the draggable grid.

Written by the indexing model from the issue text.