Fixed bug of multiple cells on rapid tapping.

Setting the longPressGestureRecognizer’s minimumPressDuration property to 0, and then rapidly tapping on cells can cause extra cells to show up that are not able to be moved in any way. This fixes that issue by disabling the longPressGestureRecognizer until the animation that happens when the long press ends.
Merge pull request #68 from timfether/master

Fixed bug of extraneous cells on rapid tapping.