Revert/undo a drop

Have been working to handle an edge case where dropping an item fails. I am processing a request on the server side using `onDrop` and if the server throws an error, I would like to "undo" the drop so the item does not stick in the destination container, but effectively moves back to the container it was dragged from.

I looked at the only other issue similar to this, which was closed some time ago, but it doesn't appear to work. I have also tried detaching the item from the container it was dropped in, and then calling `_super` but this doesnt work either.

```
onDrop: function ($item, container, _super) {
$.request('onDropItem', {
error: function(jqXHR, textStatus, errorThrown) {
// revert/undo the drop here
_super($item, container.rootGroup.itemContainer);
})
}
```

I _believe_ `container.rootGroup.itemContainer` is a reference to the container the item was selected from? I thought calling `_super()` is what performs the actual drop?

Out of desperation, I thought maybe just using the same code from `onDrop` when it is successful, but using `container.rootGroup.itemContainer` would do it, but this hasn't worked either:

```
var $clonedItem = $("