Refactoring of main menu related code

We need to make sure it's not stay active during gameplay.
Proper fix would require actually removing menu interface from GH, but then GH needs refactoring too.

client/NetPacksLobbyClient.cpp

@@ -114,7 +114,7 @@ bool LobbyStartGame::applyOnLobbyHandler(CServerHandler * handler)
 
 void LobbyStartGame::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
 {
-	CMM->showLoadingScreen(std::bind(&CServerHandler::startGameplay, handler));
+	GH.pushInt(new CLoadingScreen(std::bind(&CServerHandler::startGameplay, handler)));
 }
 
 bool LobbyUpdateState::applyOnLobbyHandler(CServerHandler * handler)