Freset: properly reset graphics objects (bug #35511) * graphics.in.h (base_graphics_object, graphics_object, root): add new method "get_factory_defaults_list" to retrieve factory defaults as property_list * graphics.in.h (base_graphics_object::reset_default_properties (void)): move definition to graphics.cc * graphics.cc (xreset_default_properties): new function to set a list of prop/val * graphics.cc (base_graphics_object::reset_default_properties): use xreset_default_properties, override with parents' defaults * graphics.cc (root_figure::reset_default_properties, figure::reset_default_properties, uitoolbar::reset_default_properties): same as above but first empty local defaults * graphics.cc (axes_figure::reset_default_properties): same as above but use "propeties.set_defaults" to reset properties to their factory value. * graphics.cc (axes_figure::properties::set_defaults): new "reset" mode, that does the same as "replace" but x/y/zlabels and title are reset instead of being deleting/recreating. * graphics.cc: add %!tests for Freset

gnulib-hg = gnulib-hg