Fix QVTKRWIBase default value

[GuillaumeFavelier]

Update the default class chosen by QVTKRenderWindowInteractor depending on the version of vtk.
The fix was suggested by @math-artist.

To reproduce, using the version 8.2 of vtk:

On my configuration, before:

>>> import pyvista
>>> import vtk
>>> vtk.qt.QVTKRenderWindowInteractor.QVTKRenderWindowInteractor.__bases__
(<class 'PyQt5.QtWidgets.QWidget'>,)

With this patch:

>>> import pyvista
>>> import vtk
>>> vtk.qt.QVTKRenderWindowInteractor.QVTKRenderWindowInteractor.__bases__
(<class 'PyQt5.QtOpenGL.QGLWidget'>,)

Closes #473

[GuillaumeFavelier]

I used vtk.vtkVersion for the check but I could use scooby too I think. Is there a way to get the major/minor version only? Maybe you know a way to do it better @banesullivan

[banesullivan]

This looks good to me!

[banesullivan]

I used vtk.vtkVersion for the check but I could use scooby too I think. Is there a way to get the major/minor version only? Maybe you know a way to do it better @banesullivan

The way you did it works well! Scooby returns the full version string so it would require extra parsing. The way you handle the version is the best way I can think of doing it