make Python Manager RAII object not singleton
Py_Finalize in destructor of singleton is problematic
MpiManager can now be made a RAII object
int main()
{
PythonEnvironment pyEnv( initFunctionThatExportsRequiredModules ); // << previously MPIManager
}
Think about having multiple PythonEnvironments ( one for each module to export ) i.e. one for core, one for LBM etc.
PythonEnvironment pyEnv( "walberla", exportForFieldEtc );
PythonEnvironment pyEnv( "lmb", lbmAndBoundaryExport );
but how to deal with "BOOST_PYTHON_MODULE( walberla_cpp )"