Bugs in building the scriptableapplication on Windows

Two small issues:

• The CMake fails since it is unable to locate shiboken2 (the executable extension is missing).
• In pyside2_config.py, the retrieval of "LIBDIR" fails since it is not set on Windows (https://stackoverflow.com/questions/47423246/get-pythons-lib-path).

I attach the patch with the required changes since I failed to setup how to push with Gerrit.