Add missing UI objects: uicontextmenu, uitoolbar, uipushtool and uitoggletool. * graphics.h.in (uicontextmenu, uitoolbar, uipushtool, uitoggletool): New graphic object classes. (uicontrol::properties::cdata): Allow "single" and "uint8" data. * graphics.cc (uitoolbar): New class implementation. * gl-render.cc (opengl_renderer::draw): Skip new object types. * plot/private/__uiobject_split_args__.m: Don't use varargin. Add parent_type and use_gcf arguments. Check that number of arguments is a multiple of 2. * plot/uicontrol.m: Adapt call to __uiobject_split_args__. * plot/uipanel.m: Likewise. * plot/uimenu.m: Rewrite to use __uiobject_split_args__. * plot/uicontextmenu.m: New file. * plot/uitoolbar.m: Likewise. * plot/uipushtool.m: Likewise. * plot/uitoggletool.m: Likewise. * plot/modules.mk (plot_FCN_FILES): Add uicontextmenu.m, uitoolbar.m, uipushtool.m and uitoggletool.m.