Core/Misc: Use proper headers to optimize compile

src/server/game/Scripting/ScriptSystem.h

@@ -5,6 +5,7 @@
 #ifndef SC_SYSTEM_H
 #define SC_SYSTEM_H
 
+#include "ScriptMgr.h"
 #include <ace/Singleton.h>
 
 #define TEXT_SOURCE_RANGE -1000000                          //the amount of entries each text source has available