[vtkusers] show correctly Itk dicom series with vtk image viewer

[John Drescher]

> Quite a bit of interaction can be done by subclassing
> vtkInteractorStyle (search vtkInteractorStyle here:
> http://www.vtk.org/Wiki/VTK/Examples#User_Interaction)
>

I find that necessary in every DICOM viewing application I write. One
reason is the default interactions (pan, zoom, 3D rotations) are not
wanted when viewing 2D slices.

John