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/mapping/MapFormatJson.cpp

@@ -767,7 +767,7 @@ CMapLoaderJson::CMapLoaderJson(CInputStream * stream)
 {
 }
 
-std::unique_ptr<CMap> CMapLoaderJson::loadMap(IGameCallback * cb)
+std::unique_ptr<CMap> CMapLoaderJson::loadMap(CPrivilegedInfoCallback * cb)
 {
 	LOG_TRACE(logGlobal);
 	auto result = std::make_unique<CMap>(cb);