BUG 13875: Add a separate python module to resolve dependencies.

The dependency of Rendering/Matplotlib on Wrapping/Python was causing
the latter module to be configured too early.  Wrapping/Python must
be configured after all wrapped modules or it will not be able to capture
all of the wrapped modules properly.

The solution is to create a new Python vtk-module that both Wrapping/Python
and Rendering/Matplotlib can depend on.

Change-Id: I8348fd80147126866dec91488cb0771a7f412636
Merge topic 'python-module' into master

146e2f78 BUG 13875: Add a separate python module to resolve dependencies.