Implement copy and move for tree like components.
| copy | makes a copy of an item |
| move | moves an item to a new position |
| moveBottom | moves the specified item to the last position |
| moveDown | moves an element downwards within its current branch |
| moveTop | moves the specified item to the first position |
| moveUp | moves an element upwards within its current branch |
| $dropAllow | can be redefined, if you need custom drop rules |