[j.sig2] std::optional gProjectDocument -> unique_ptr gDoc ()

GUI/Model/Project/ProjectDocument.cpp

GUI/Model/Project/ProjectDocument.h

GUI/View/Access/DataPropertyWidget.cpp

GUI/View/Canvas/IntensityDataCanvas.cpp

GUI/View/Canvas/MaskEditorActions.cpp

GUI/View/Canvas/MaskEditorCanvas.cpp

GUI/View/Canvas/ProjectionsEditorCanvas.cpp

GUI/View/Canvas/SpecularDataCanvas.cpp

GUI/View/Combo/ItemComboToolbar.cpp

GUI/View/Data/DatafilesSelector.cpp

GUI/View/Device/AxisPropertyForm.cpp

GUI/View/Device/SpanPropertyForm.cpp

GUI/View/FitControl/MinimizerSettingsWidget.cpp

GUI/View/FitControl/RunFitControlWidget.cpp

GUI/View/Frame/Fit1DFrame.cpp

GUI/View/Frame/Fit2DFrame.cpp

GUI/View/Instrument/InstrumentLibraryEditor.cpp

GUI/View/Job/JobView.cpp

GUI/View/JobControl/JobListModel.cpp

GUI/View/JobControl/JobListing.cpp