Add stub facilities, institutions, and regions.
Rename stub institution models into null institutions
Rename stub region files into null region files
Rename stub facility into sink facility
Rename stub facility into source facility
Implementation of null institution.
Implementation of a basic region model from stubs.
Implementation of a sink facility from stubs.
Initital iplementation of source facility.
Cmake instructions for Models.
Empty CMakeLists for integration_tests is created.
Modified CmakeList to get models into building process.