COMP: Update importing of wrapped VTK classes for VTK 7

Python wrapped objects in VTK 7 are now new-style Python classes. Subsequently,
the type of a wrapped class is now the built-in 'type', whereas in VTK 6 it was
'vtkclass'. Compare the following output for VTK 6 and VTK 7:

>>> vtk.VTK_MAJOR_VERSION, type(vtk.vtkObjectBase)
(6, <type 'vtkclass'>)

>>> vtk.VTK_MAJOR_VERSION, type(vtk.vtkObjectBase)
(7, <type 'type'>)

This commit updates the importing of wrapped VTK classes to account for the new
behavior. Instead of checking for the type name to equal 'vtkclass', importing
now checks whether the type is a subclass of vtkObjectBase.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25225 3bd1e089-480b-0410-8dfb-8563597acbee