improved icosn for the GUI (higher contrast) * libgui/src/icons/octave/128x128/edit-redo.png * libgui/src/icons/octave/128x128/go-down.png * libgui/src/icons/octave/128x128/go-first.png * libgui/src/icons/octave/128x128/go-last.png * libgui/src/icons/octave/128x128/go-next.png * libgui/src/icons/octave/128x128/go-previous.png * libgui/src/icons/octave/128x128/go-up.png * libgui/src/icons/octave/128x128/plot-xy-curve.png * libgui/src/icons/octave/128x128/system-run.png * libgui/src/icons/octave/scalable/edit-redo.svg * libgui/src/icons/octave/scalable/go-down.svg * libgui/src/icons/octave/scalable/go-first.svg * libgui/src/icons/octave/scalable/go-last.svg * libgui/src/icons/octave/scalable/go-next.svg * libgui/src/icons/octave/scalable/go-previous.svg * libgui/src/icons/octave/scalable/go-up.svg * libgui/src/icons/octave/scalable/plot-xy-curve.svg

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