Completely remove IGameCallback class

- CClient now inherits directly from CPrivilegedInfoCallback, like
IGameCallback did before. However CClient no longer needs dummy
implementation of IGameEventCallback
- CGObjectInstance hierarchy now uses CPrivilegedInfoCallback for
callback. Actual events can only be emitted in calls that receive
IGameEventCallback pointer, e.g. heroVisit
- CGameHandler now inherits directly from both CPrivilegedInfoCallback
and IGameEventCallback as it did before via IGameCallback

lib/rmg/CMapGenerator.h

@@ -23,7 +23,7 @@ class RmgMap;
 class CMap;
 class Zone;
 class CZonePlacer;
-class IGameCallback;
+class CPrivilegedInfoCallback;
 
 using JsonVector = std::vector<JsonNode>;
 
@@ -54,7 +54,7 @@ public:
 		bool singleThread;
 	};
 	
-	explicit CMapGenerator(CMapGenOptions& mapGenOptions, IGameCallback * cb, int RandomSeed);
+	explicit CMapGenerator(CMapGenOptions& mapGenOptions, CPrivilegedInfoCallback * cb, int RandomSeed);
 	~CMapGenerator(); // required due to std::unique_ptr
 	
 	const Config & getConfig() const;