Add confirmation and removal to bindings menu

This makes the following improvements to the gamepad bindings menu:

- The menu now shows a hint that you can press a button while any of
  the bind options are selected (or that you can navigate away from
  those options)
- Instead of button presses immediately setting a binding, they now
  ask for confirmation: press the same button a second time to confirm
- You can now remove a binding, the same way you add it (this has the
  same type of confirmation)
- This menu used to be inconsistent with pretty much every other menu
  in the game by showing a permanent title and description for the menu
  itself ("Game Pad", "Change controller options.") rather than showing
  a title and description for the currently selected option.
  This inconsistency is now fixed.

desktop_version/src/ButtonGlyphs.h

@@ -20,6 +20,7 @@ void BUTTONGLYPHS_keyboard_set_active(bool active);
 void BUTTONGLYPHS_update_layout(SDL_GameController *c);
 
 const char* BUTTONGLYPHS_get_wasd_text(void);
+const char* BUTTONGLYPHS_sdlbutton_to_glyph(SDL_GameControllerButton button);
 const char* BUTTONGLYPHS_get_button(ActionSet actionset, Action action, int binding);
 
 char* BUTTONGLYPHS_get_all_gamepad_buttons(