Move an item up in the list.

        Essentially swap it with the item above it.

        :param item: The item to be moved.

def move_item_up(self, item):
        """Move an item up in the list.

        Essentially swap it with the item above it.

        :param item: The item to be moved.
        """
        prev_iter = self._prev_iter_for(item)
        if prev_iter is not None:
            self.model.swap(prev_iter, self._iter_for(item))