wxToolBarBase: add prepend_ methods (they do not exist in wxwidgets
itself but are nice calls to the insert_ methods)
document all (add|insert|prepend)_(normal|check|radio|control) methods
wxMenu: make the _menu methods extra from the _normal methods. add some
checks that the title may not be empty and raise exceptions if that
happens.
document all (add|insert|prepend)_(normal|check|radio|menu) methods
sample/dialog: use correctly WX::Menu#append_menu instead of
WX::Menu#append_normal