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.cpp

@@ -272,7 +272,7 @@ const char* BUTTONGLYPHS_get_wasd_text(void)
     return loc::gettext("Press left/right to move");
 }
 
-static const char* sdlbutton_to_glyph(const SDL_GameControllerButton button)
+const char* BUTTONGLYPHS_sdlbutton_to_glyph(const SDL_GameControllerButton button)
 {
     if (button > SDL_CONTROLLER_BUTTON_RIGHTSHOULDER)
     {
@@ -292,7 +292,7 @@ static const char* glyph_for_vector(
         return NULL;
     }
 
-    return sdlbutton_to_glyph(buttons[index]);
+    return BUTTONGLYPHS_sdlbutton_to_glyph(buttons[index]);
 }
 
 const char* BUTTONGLYPHS_get_button(const ActionSet actionset, const Action action, int binding)