cta-statistics-save now gather the statistics from the catalogue

statistics/CMakeLists.txt

statistics/FileStatistics.cpp

statistics/FileStatistics.hpp

statistics/Statistics.cpp

statistics/Statistics.hpp

statistics/StatisticsGetter.cpp

statistics/StatisticsGetter.hpp

statistics/StatisticsSaveCmd.cpp

statistics/StatisticsSaveCmdLineArgs.cpp

statistics/StatisticsUpdateCmd.cpp

statistics/StatisticsUpdater.cpp

statistics/StatisticsUpdater.hpp