Function nav_context 

pub fn nav_context<A: MenuAction<Message = Message>, L: Into<Cow<'static, str>> + From<&'static str> + 'static, Message: 'static + Clone>(
    key_binds: &HashMap<KeyBind, A>,
    children: Vec<Vec<MenuItem<A, L>>>,
) -> Vec<MenuTree<Message>>

Create a menu tree from a widget and a vector of sub trees