Add a delay after drop

[dcporter44]

If I drop an element, I have to then re-sort the tree to reflect the new order. With large trees, this resorting can take a second or so. This means that after I drop an element, it returns to its original position, and then waits for my re-sorting to be done, and then it adjusts to its new position. This flicker of movement is very annoying.

It would be ideal if on drop, the item stayed in its dropped position for around 2 seconds or so. This would prevent the flicker.

react-beautiful-dnd implemented it this way and it works really great.