Begin few code reorganization

src/utils/checkpointing/CMakeLists.txt

src/utils/checkpointing/ReadIBoundaryConditionDescriptor.cpp

src/utils/checkpointing/ReadIBoundaryConditionDescriptor.hpp

src/utils/checkpointing/ReadIBoundaryDescriptor.cpp

src/utils/checkpointing/ReadIBoundaryDescriptor.hpp

src/utils/checkpointing/ReadItemArray.hpp

src/utils/checkpointing/ReadItemArrayVariant.cpp

src/utils/checkpointing/ReadItemArrayVariant.hpp

src/utils/checkpointing/ReadItemValue.hpp

src/utils/checkpointing/ReadItemValueVariant.cpp

src/utils/checkpointing/ReadItemValueVariant.hpp

src/utils/checkpointing/ReadSubItemArrayPerItemVariant.cpp

src/utils/checkpointing/ReadSubItemArrayPerItemVariant.hpp

src/utils/checkpointing/ReadSubItemValuePerItemVariant.cpp

src/utils/checkpointing/ReadSubItemValuePerItemVariant.hpp

src/utils/checkpointing/ResumeUtils.cpp