[vtkusers] how to use a QVTKWidget with QStackWidget

[José M. Rodriguez Bacallao]

hi folks, I am trying to use QVTKWidget with QStackwidget but I am
getting a lot of flicker, how do I setup a correct pipeline with
QVTKWidget and QStackQiwdget, my current test pipeline is something
like:

vtkGDCMImageReader -> vtkImageViewer2 -> QVTKWidget