Menu of components (#131)

Allow Container::Vertical and Container::Horizontal to have an
external selector, similar to Container::Tab.

This is useful for implementing a menu of menu.

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

doc/example_list.md

@@ -35,6 +35,7 @@
 @example ./examples/component/input.cpp
 @example ./examples/component/homescreen.cpp
 @example ./examples/component/radiobox.cpp
+@example ./examples/component/menu_multiple.cpp
 @example ./examples/component/slider_rgb.cpp
 @example ./examples/component/menu.cpp
 @example ./examples/component/menu_style.cpp