model: Finalizing implementation of FaceMetric::Status tracing

Adding test case (ndnSIM-fib-entry), which can be used as an example how
to set up tracing.
diff --git a/model/fw/green-yellow-red.h b/model/fw/green-yellow-red.h
index 371f7fd..e82c93b 100644
--- a/model/fw/green-yellow-red.h
+++ b/model/fw/green-yellow-red.h
@@ -47,13 +47,16 @@
                        Ptr<const InterestHeader> header,
                        Ptr<const Packet> origPacket,
                        Ptr<pit::Entry> pitEntry);
+
+  virtual void
+  WillEraseTimedOutPendingInterest (Ptr<pit::Entry> pitEntry);
+
   virtual void
   DidReceiveValidNack (Ptr<Face> incomingFace,
                        uint32_t nackCode,
                        Ptr<const InterestHeader> header,
                        Ptr<const Packet> origPacket,
                        Ptr<pit::Entry> pitEntry);
-
 private:
   typedef Nacks super;
 };