[CSM] Client side modding

* rename GameScripting to ServerScripting
* Make getBuiltinLuaPath static serverside
* Add on_shutdown callback
* Add on_receiving_chat_message & on_sending_chat_message callbacks
* ScriptApiBase: use IGameDef instead of Server
  This permits to share common attribute between client & server
* Enable mod security in client side modding without conditions

src/script/lua_api/l_env.h

@@ -242,7 +242,7 @@ class LuaLBM : public LoadingBlockModifierDef
 };
 
 struct ScriptCallbackState {
-	GameScripting *script;
+	ServerScripting *script;
 	int callback_ref;
 	int args_ref;
 	unsigned int refcount;