Volume rendering now updated when volume node geometry is updated
To address issue 4023 the vtkMRMLVolumeRenderingDisplayableManager now observes the vtkCommand::Modified event on any rendered vtkMRMLVolumeNode
To address issue 4023 the vtkMRMLVolumeRenderingDisplayableManager now observes the vtkCommand::Modified event on any rendered vtkMRMLVolumeNode