Refactored Statistics get, update, save with reusable code

statistics/CMakeLists.txt

statistics/DatabaseStatisticsService.cpp

statistics/DatabaseStatisticsService.hpp

statistics/DatabaseStatisticsServiceFactory.cpp

statistics/DatabaseStatisticsServiceFactory.hpp

statistics/MySQLStatisticsService.cpp

statistics/MySQLStatisticsService.hpp

statistics/StatisticsGetter.cpp

statistics/StatisticsSaveCmd.cpp

statistics/StatisticsService.cpp

statistics/StatisticsService.hpp

statistics/StatisticsServiceFactory.cpp

statistics/StatisticsServiceFactory.hpp

statistics/StatisticsUpdateCmd.cpp