## Add option RectangularShape to vtkFinitePlaneRepresentation

Using the option `RectangularShape` on the
`vtkFinitePlaneRepresentation` for the `vtkFinitePlaneWidget`, the
widget stays rectangular when moving the two control points v1 and
v1. In this way, the user can adjust the width and height of the
widget rather than changing its shape to be a parallelogram.
