Introduce Options and use them for Menu.

Introduce Options for components. This allows me to add new features,
without updating functions signatures.

include/ftxui/component/component_options.hpp

@@ -0,0 +1,19 @@
+#ifndef FTXUI_COMPONENT_COMPONENT_OPTIONS_HPP
+#define FTXUI_COMPONENT_COMPONENT_OPTIONS_HPP
+
+namespace ftxui {
+
+struct MenuOption {
+  Decorator normal_style = nothing;
+  Decorator focused_style = inverted;
+  Decorator selected_style = bold;
+  Decorator selected_focused_style = focused_style | selected_style;
+
+  // State update callback.
+  std::function<void()> on_change = []() {};
+  std::function<void()> on_enter = []() {};
+};
+
+};     // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_COMPONENT_OPTIONS_HPP */