when an item is added to the layout, give it a chance to react. in the case of Widget, we're going to set the movable state of the QGraphicsItem. the result: items move, or don't, based on whether or not they are in a layout. finally, you can't just move shit around in the panel.

it's pretty hackish since we have to special case FreeLayout but hey, since when were layouts in plasma ever sane?