New DetectorItem::setSize to hide axes details from ImportDataAssistant.

GUI/coregui/Models/DetectorItems.h

GUI/coregui/Models/InstrumentItem.cpp

GUI/coregui/Models/InstrumentItem.h

GUI/coregui/Models/JobModelFunctions.cpp

GUI/coregui/Models/RectangularDetectorItem.cpp

GUI/coregui/Models/RectangularDetectorItem.h

GUI/coregui/Models/SphericalDetectorItem.cpp

GUI/coregui/Models/SphericalDetectorItem.h

GUI/coregui/Views/ImportDataWidgets/ImportDataAssistant.cpp

...coregui/Views/ImportDataWidgets/LinkInstrumentManager.cpp

...oregui/Views/InstrumentWidgets/InstrumentEditorWidget.cpp