SSB-42: splitting datacontainers class in multiple files

.gitattributes

CAL/CalibrationCommon/lib/CMakeLists.txt

CAL/CalibrationCommon/lib/datacontainers/__init__.py

...alibrationCommon/lib/datacontainers/holography_dataset.py

...tionCommon/lib/datacontainers/holography_specification.py

CAL/CalibrationCommon/lib/datacontainers/measurementset.py

CAL/CalibrationCommon/lib/utils.py

CAL/CalibrationCommon/test/t_holography_dataset_class.py