Rewrote ScreenSystemOverlay overlay/default.lua to be able to display multiple messages. Added Reload Overlay Screens option to debug menu.

src/ScreenManager.h

@@ -51,6 +51,7 @@ public:
 	void RefreshCreditsMessages();
 	void ThemeChanged();
 	void ReloadOverlayScreens();
+	void ReloadOverlayScreensAfterInputFinishes();
 
 	/**
 	 * @brief Is this Screen in the main Screen stack, but not the bottommost Screen?
@@ -79,6 +80,10 @@ private:
 	// operations take a long time, and will cause a skip on the next update.
 	bool		m_bZeroNextUpdate;
 
+	// This exists so the debug overlay can reload the overlay screens without seg faulting.
+	// It's "AfterInput" because the debug overlay carries out actions in Input.
+	bool m_bReloadOverlayScreensAfterInput;
+
 	Screen *MakeNewScreen( const RString &sName );
 	void LoadDelayedScreen();
 	bool ActivatePreparedScreenAndBackground( const RString &sScreenName );