Entities redesign and a few ERM features

* Made most Handlers derived from CHandlerBase and moved service API there.
* Declared existing Entity APIs.
* Added basic script context caching
* Started Lua script module
* Started Lua spell effect API
* Started script state persistence
* Started battle info callback binding
* CommitPackage removed
* Extracted spells::Caster to own header; Expanded Spell API.
* implemented !!MC:S, !!FU:E, !!FU:P, !!MA, !!VR:H, !!VR:C
* !!BU:C, !!BU:E, !!BU:G, !!BU:M implemented
* Allow use of "MC:S@varName@" to declare normal variable (technically v-variable with string key)
* Re-enabled VERM macros.
* !?GM0 added
* !?TM implemented
* Added !!MF:N
* Started !?OB, !!BM, !!HE, !!OW, !!UN
* Added basic support of w-variables
* Added support for ERM indirect variables
* Made !?FU regular trigger
* !!re (ERA loop receiver) implemented
* Fixed ERM receivers with zero args.

scripting/lua/api/events/SubscriptionRegistryProxy.cpp

@@ -0,0 +1,28 @@
+/*
+ * SubscriptionRegistryProxy.cpp, 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
+ *
+ */
+#include "StdInc.h"
+
+#include "SubscriptionRegistryProxy.h"
+
+#include "../Registry.h"
+
+namespace scripting
+{
+namespace api
+{
+namespace events
+{
+//No methods here, just an empty metatable for type safety.
+VCMI_REGISTER_CORE_SCRIPT_API(EventSubscriptionProxy, "EventSubscription");
+const std::vector<EventSubscriptionProxy::RegType> EventSubscriptionProxy::REGISTER = {};
+const std::vector<EventSubscriptionProxy::CustomRegType> EventSubscriptionProxy::REGISTER_CUSTOM = {};
+}
+}
+}