Update IRefCounted & fix missing includes on some headers (#421)

game/shared/igamesystem.h

@@ -13,6 +13,9 @@
 
 #include "network_connection.pb.h"
 #include "iloopmode.h"
+#include "entityhandle.h"
+#include "entity2/entityidentity.h"
+#include "tier1/utlstring.h"
 
 /*
 * AMNOTE: To create your own gamesystem, you need to inherit from CBaseGameSystem or CAutoGameSystem,

public/iloopmode.h

@@ -14,6 +14,7 @@
 #include <inputsystem/InputEnums.h>
 #include <KeyValues.h>
 #include <engine/eventdispatcher.h>
+#include <tier1/convar.h>
 
 class ISource2WorldSession;
 class ISceneView;

public/tier1/refcount.h

@@ -23,6 +23,7 @@
 class IRefCounted
 {
 public:
+	virtual ~IRefCounted() {}
 	virtual int AddRef() = 0;
 	virtual int Release() = 0;
 };