GameHandler now uses GameConnectionID instead of connection pointers

lib/serializer/GameConnectionID.h

@@ -0,0 +1,20 @@
+/*
+ * GameConnectionID.h, part of VCMI engine
+ *
+ * Authors: listed in file AUTHORS in main folder
+ *
+ * License: GNU General Public License v2.0 or later
+ * Full text of license available in license.txt file, in main folder
+ *
+ */
+#pragma once
+
+VCMI_LIB_NAMESPACE_BEGIN
+
+enum class GameConnectionID : int8_t
+{
+	INVALID = -1,
+	FIRST_CONNECTION = 1
+};
+
+VCMI_LIB_NAMESPACE_END