make stand-alone windows from dock widgets when floating (bug #38785) * octave-dock-widget.cc: new file, (constructor): moved from octave-dock-widget.h, disable floating and closing by qt, add custom title bar with buttons for closing and floating, (destructor): saving state and geometry depending on state, (set_title): new function for setting the title of the custom title bar, (make_window): make dock widget a stand-alone window by reparenting to 0 and restore last geometry, (make_widget): readd the widget to the main window, the last position and size can not be restored due to previous reparenting (change_floating): slot for dock button in title bar (change_visibility): slot for hiding the widget * octave-dock-widget.h: removed signal connection and slot for floating by qt, moved constructor to *.cc, declaration of new functions and slots (main_win): new function returning the main window * main-window.cc(notice-settings): when updating icons, use a list of all dock widgets instead of searching childrens that may have set their parent to 0 (set_window_layout): use make_window instead of setWindowsFlag for floating, do not use grouping in settings because of possibly nested groups (write_settings): saving the state and geometry of the dock-widgets is moved into the dock widget's destructors main-window.n(dock_widget_list): function returning a list of all dock widgets * documentation-dock-widget.cc, files-dock-widget.cc, history-dock-widget.cc, file-editor.cc, terminal-dock-widget.cc, workspace-view.cc: use new function set_title instead of setWindowTitle * files-dock-widget.cc, file-editor.cc, : replace parent () by main_win () * widget-dock.png, widget-undock.png, widget-close.png: new icons * resource.qrc: new icons widget-dock.png, widget-undock.png, widget-close.png * module-mk: new icons widget-dock.png, widget-undock.png, widget-close.png and new file octave-dock-widget.cc