gtk3x: help_vgrid support functions
Rename gtk3x-client helpdlg widget 'help_vbox' as 'help_vgrid'. Add and use support functions help_box_add() and help_box_clear() to handle it, instead of gtk_container_add() calls. This prepares it for gtk-3.98.4 where GtkContainer gets dropped.
New version implements help_box_clear() without gtk_container_foreach()
Rename gtk3x-client helpdlg widget 'help_vbox' as 'help_vgrid'. Add and use support functions help_box_add() and help_box_clear() to handle it, instead of gtk_container_add() calls. This prepares it for gtk-3.98.4 where GtkContainer gets dropped.