Hidden observeADSnotifications switch in WorkspaceGroup. Re #7253.

Code/Mantid/Framework/API/inc/MantidAPI/WorkspaceGroup.h

Code/Mantid/Framework/API/src/Algorithm.cpp

Code/Mantid/Framework/API/src/AnalysisDataService.cpp

Code/Mantid/Framework/API/src/MultiPeriodGroupAlgorithm.cpp

Code/Mantid/Framework/API/src/WorkspaceGroup.cpp

Code/Mantid/Framework/Algorithms/src/GroupWorkspaces.cpp

Code/Mantid/Framework/DataHandling/src/LoadSassena.cpp