Apply patch 8 from issue #13 - modernise use of override

externals/qtcolorpicker/src/qtcolorpicker.h

src/common/Session.hpp

src/core/Core.hpp

src/interface/Interface_graphic.hpp

src/interface/Interval_select.hpp

src/interface/Node_select.hpp

src/interface/Settings_window.hpp

src/interface/qxtspanslider.h

src/interface/viteqtreewidget.hpp

src/parser/PajeParser/PajeFileManager.hpp

src/parser/PajeParser/ParserPaje.hpp

src/parser/PajeParser/ParserVite.hpp

src/parser/PajeParser/mt_PajeFileManager.hpp

src/parser/PajeParser/mt_ParserEventPaje.hpp

src/parser/PajeParser/mt_ParserPaje.hpp

src/parser/Parser.hpp

src/parser/TauParser/ParserTau.hpp

src/plugin/Plugin_window.hpp

src/render/GanttDiagram.hpp

src/render/Hook_event.hpp