Continue code cleaning and organization

src/language/modules/CoreModule.cpp

src/language/modules/MeshModule.cpp

src/language/modules/SchemeModule.cpp

src/language/modules/WriterModule.cpp

src/utils/checkpointing/CMakeLists.txt

src/utils/checkpointing/CheckpointUtils.cpp

src/utils/checkpointing/CheckpointUtils.hpp

src/utils/checkpointing/DiscreteFunctionTypeHFType.hpp

src/utils/checkpointing/DualMeshTypeHFType.hpp

...tils/checkpointing/IBoundaryConditionDescriptorHFType.hpp

src/utils/checkpointing/IBoundaryDescriptorHFType.hpp

src/utils/checkpointing/IInterfaceDescriptorHFType.hpp

src/utils/checkpointing/INamedDiscreteDataHFType.hpp

src/utils/checkpointing/IWriterHFType.hpp

src/utils/checkpointing/IZoneDescriptorHFType.hpp

src/utils/checkpointing/ItemTypeHFType.hpp

src/utils/checkpointing/LinearSolverOptionsHFType.hpp

src/utils/checkpointing/OStreamTypeHFType.hpp

src/utils/checkpointing/ParallelCheckerHFType.hpp

src/utils/checkpointing/QuadratureTypeHFType.hpp