Implement preview music properly as a new optional tag in the ssc file. Changed ScreenManager to emit an error instead of asserting if a screen attempts to use SetNewScreen inside an InitCommand. Changed decorations layer to be a proper child instead of stripping away the ActorFrame.

src/ScreenManager.cpp

@@ -742,7 +742,12 @@ void ScreenManager::LoadDelayedScreen()
 		// Screens may not call SetNewScreen from the ctor or Init(). (We don't do this
 		// check inside PrepareScreen; that may be called from a thread for concurrent
 		// loading, and the main thread may call SetNewScreen during that time.)
-		ASSERT_M( m_sDelayedScreen.empty(), m_sDelayedScreen );
+		// Emit an error instead of asserting. -Kyz
+		if(!m_sDelayedScreen.empty())
+		{
+			LuaHelpers::ReportScriptError("Setting a new screen during an InitCommand is not allowed.");
+			m_sDelayedScreen= "";
+		}
 
 		bLoaded = ActivatePreparedScreenAndBackground( sScreenName );
 		ASSERT( bLoaded );