add GetPlayMode Lua method

stepmania/src/GameState.cpp

@@ -1869,6 +1869,7 @@ public:
 	}
 	static int GetPreferredDifficulty( T* p, lua_State *L )	{ lua_pushnumber(L, p->m_PreferredDifficulty[IArg(1)] ); return 1; }
 	static int AnyPlayerHasRankingFeats( T* p, lua_State *L )	{ lua_pushboolean(L, p->AnyPlayerHasRankingFeats() ); return 1; }
+	static int GetPlayMode( T* p, lua_State *L )	{ lua_pushnumber(L, p->m_PlayMode ); return 1; }
 
 	static void Register(lua_State *L)
 	{
@@ -1890,6 +1891,7 @@ public:
 		ADD_METHOD( GetEditSourceSteps )
 		ADD_METHOD( GetPreferredDifficulty )
 		ADD_METHOD( AnyPlayerHasRankingFeats )
+		ADD_METHOD( GetPlayMode )
 		Luna<T>::Register( L );
 
 		// Add global singleton if constructed already.  If it's not constructed yet,