eliminate unnecessary uses of octave_qobject in GUI classes * BaseControl.cc, BaseControl.h, ButtonControl.cc, ButtonControl.h, ButtonGroup.cc, ButtonGroup.h, Canvas.cc, Canvas.h, CheckBoxControl.cc, CheckBoxControl.h, Container.cc, Container.h, ContextMenu.cc, ContextMenu.h, EditControl.cc, EditControl.h, Figure.cc, Figure.h, GLCanvas.cc, GLCanvas.h, ListBoxControl.cc, ListBoxControl.h, Menu.cc, Menu.h, Object.cc, Object.h, Panel.cc, Panel.h, PopupMenuControl.cc, PopupMenuControl.h, PushButtonControl.cc, PushButtonControl.h, PushTool.cc, PushTool.h, RadioButtonControl.cc, RadioButtonControl.h, SliderControl.cc, SliderControl.h, Table.cc, Table.h, TextControl.cc, TextControl.h, ToggleButtonControl.cc, ToggleButtonControl.h, ToggleTool.cc, ToggleTool.h, ToolBar.cc, ToolBar.h, ToolBarButton.cc, ToolBarButton.h, annotation-dialog.cc, annotation-dialog.h, qt-graphics-toolkit.cc, qt-graphics-toolkit.h, command-widget.h, community-news.cc, community-news.h, documentation-bookmarks.cc, documentation-bookmarks.h, documentation.cc, external-editor-interface.cc, external-editor-interface.h, find-files-dialog.cc, find-files-dialog.h, graphics-init.cc, graphics-init.h, interpreter-qobject.cc, file-editor.cc, find-dialog.cc, find-dialog.h, main-window.cc, main-window.h, news-reader.cc, news-reader.h, octave-qobject.cc, release-notes.cc, resource-manager.cc, set-path-dialog.cc, set-path-dialog.h, shortcut-manager.cc, shortcut-manager.h, welcome-wizard.cc, welcome-wizard.h, workspace-model.cc: Don't store references to octave_qobject in GUI classes where it is no longer needed. Eliminate unnecessary octave_qobject constructor arguments. Change all uses.

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%!test <*55322>
%! hf = figure ("visible", "off");
%! unwind_protect
%!   hax = axes ("parent", hf);
%!   hg = hggroup ();
%!   hl = line (hax, [0, 1], [1, 1], "parent", hax, "parent", hg);
%!   assert (get (hax, "children"), hg);
%!   assert (get (hg, "children"), hl);
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect