Migrate python wrapping to latest MITK developments

The two following CMake cache variables were removed:

• WRAP_DEFAULT
• WRAP_PYTHON

Instead, the following variable was introduced:

• MITK_WRAP_PYTHON

In contrast to before, it is ON by default, when the following two variables are ON:

• MITK_USE_SWIG
• MITK_USE_Python3

To summarize, to enable Python wrapping, simply switch on MITK_USE_SWIG and MITK_USE_Python3.