provide XML::writeTaggedElement and use it

GUI/Model/Beam/BeamDistributionItem.cpp

GUI/Model/Beam/GrazingScanItem.cpp

GUI/Model/Beam/SourceItems.cpp

GUI/Model/Data/Data2DItem.cpp

GUI/Model/Data/DataItem.cpp

GUI/Model/Detector/DetectorItem.cpp

GUI/Model/Detector/OffspecDetectorItem.cpp

GUI/Model/Job/JobItem.cpp

GUI/Model/Mask/MaskItems.cpp

GUI/Model/Material/MaterialItem.cpp

GUI/Model/Material/MaterialsSet.cpp

GUI/Model/Mini/MinimizerItems.cpp

GUI/Model/Par/ParameterTreeItems.cpp

GUI/Model/Sample/CoreAndShellItem.cpp

GUI/Model/Sample/InterferenceItems.cpp

GUI/Model/Sample/ItemWithParticles.cpp

GUI/Model/Sample/LayerItem.cpp

GUI/Model/Sample/MesocrystalItem.cpp

GUI/Model/Sample/ParticleItem.cpp

GUI/Model/Sample/ParticleLayoutItem.cpp