Currently, when a new PlanarFIgure is created within QmitkMeasurement, an PlanarFigureInteractor is created as well and activated permanently, i.e., the PlanarFigure can be interacted with until the application closes.

This should be restricted to allow interactions only as long as QmitkMeasurement is active/visible.

Also, when loading PlanarFigures and QmitkMeasurement is active, the newly loaded figures should also become interactable. Currently, this is not the case since no-one creates an interactor for them. This could be done by listening to DataStorage changes and create an interactor for all figures which do not already have one (from within QmitkMeasurement).