restore (un)docking of widgets without reparenting on non-windows systems * octave-dock-widget.cc(constructor): dock widgets features depending on system; (destructor): update comment; (set_title): set title in user defined title bar widget only on windows; (make_window): just set the windows flag when floating on non-windows systems; (make_widget): just set the widget flag when docked on non-windows systems; (change_floating): detect actual state from related flag on non-windows sys.; * main-window.cc(set_window_layout): use correct setting categorie for geometry

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