[checksum] Adds cta::checksum namespace

catalogue/ArchiveFileRow.hpp

catalogue/CatalogueTest.cpp

catalogue/OracleCatalogue.hpp

catalogue/PostgresCatalogue.hpp

catalogue/TapeFileWritten.hpp

common/CMakeLists.txt

common/checksum/ChecksumBlob.cpp

common/checksum/ChecksumBlob.hpp

common/checksum/ChecksumBlobSerDeser.hpp

common/checksum/ChecksumBlobTest.cpp

common/dataStructures/ArchiveFile.hpp

common/dataStructures/ArchiveFileTest.cpp

common/dataStructures/ArchiveRequest.hpp

common/dataStructures/TapeFile.hpp

objectstore/AlgorithmsTest.cpp

objectstore/GarbageCollectorTest.cpp

scheduler/SchedulerDatabaseTest.cpp

scheduler/SchedulerTest.cpp

...castor/tape/tapeserver/daemon/DataTransferSessionTest.cpp

...stor/tape/tapeserver/daemon/MigrationReportPackerTest.cpp