Fix lua raid GetGroup(client) and add lua raid GetGroupNumber(index)

This number will return group number and not let us iterate a bunch of
times to verify group numbers

zone/lua_raid.h

@@ -47,6 +47,7 @@ public:
 	void TeleportRaid(Lua_Mob sender, uint32 zone_id, uint32 instance_id, float x, float y, float z, float h);
 	int GetID();
 	Lua_Client GetMember(int index);
+	int GetGroupNumber(int index);
 };
 
 #endif