Added functionality for classification

CMakeLists.txt

src/CMakeLists.txt

src/descriptor_identifier/Model/Model.cpp

src/descriptor_identifier/Model/Model.hpp

src/descriptor_identifier/Model/ModelClassifier.cpp

src/descriptor_identifier/Model/ModelClassifier.hpp

src/descriptor_identifier/Model/ModelRegressor.cpp

src/descriptor_identifier/Model/ModelRegressor.hpp

src/descriptor_identifier/SISSO_DI/SISSOClassifier.cpp

src/descriptor_identifier/SISSO_DI/SISSOClassifier.hpp

src/descriptor_identifier/SISSO_DI/SISSORegressor.cpp

src/descriptor_identifier/SISSO_DI/SISSORegressor.hpp

src/descriptor_identifier/SISSO_DI/SISSO_DI.cpp

src/descriptor_identifier/SISSO_DI/SISSO_DI.hpp

src/python/bindings_docstring_keyed.cpp

src/python/bindings_docstring_keyed.hpp

src/python/descriptor_identifier/SISSOClassifier.cpp

src/python/descriptor_identifier/SISSORegressor.cpp

src/python/descriptor_identifier/SISSO_DI.cpp

tests/test_descriptor_identifier/test_model.py