[j.sig2] make full use of gDoc being global ()

GUI/View/Data/DataView.cpp

GUI/View/Data/DataView.h

GUI/View/Data/DatafileEditor.cpp

GUI/View/Data/DatafileEditor.h

GUI/View/Data/DatafilesSelector.cpp

GUI/View/Data/DatafilesSelector.h

GUI/View/Instrument/InstrumentListModel.cpp

GUI/View/Instrument/InstrumentListModel.h

GUI/View/Instrument/InstrumentListing.cpp

GUI/View/Instrument/InstrumentListing.h

GUI/View/Instrument/InstrumentView.cpp

GUI/View/Instrument/InstrumentView.h

GUI/View/Job/JobProgressAssistant.cpp

GUI/View/Job/JobProgressAssistant.h

GUI/View/Job/JobView.cpp

GUI/View/Job/JobView.h

GUI/View/Main/MainWindow.cpp

GUI/View/Manager/ProjectLoadProblemDialog.cpp

GUI/View/Manager/ProjectLoadProblemDialog.h

GUI/View/Manager/ProjectManager.cpp