Refs #3316: Saving and loading of a MDGridBox to NXS.

Code/Mantid/Framework/MDEvents/inc/MantidMDEvents/IMDBox.h

Code/Mantid/Framework/MDEvents/inc/MantidMDEvents/MDBox.h

Code/Mantid/Framework/MDEvents/inc/MantidMDEvents/MDEvent.h

.../Mantid/Framework/MDEvents/inc/MantidMDEvents/MDGridBox.h

Code/Mantid/Framework/MDEvents/src/IMDBox.cpp

Code/Mantid/Framework/MDEvents/src/MDBox.cpp

Code/Mantid/Framework/MDEvents/src/MDGridBox.cpp

Code/Mantid/Framework/MDEvents/test/IMDBoxTest.h

Code/Mantid/Framework/MDEvents/test/MDBoxTest.h

Code/Mantid/Framework/MDEvents/test/MDGridBoxTest.h

Code/Mantid/Framework/Nexus/inc/MantidNexus/NeXusFile.hpp