model: Major API changes

Interest and ContentObject are no longer derived from Header class.
Instead, they are encapsulating payload and, optionally, wire-formatted
Packet object.

Refs #1005 (http://redmine.named-data.net/)
diff --git a/model/fw/green-yellow-red.cc b/model/fw/green-yellow-red.cc
index 5d6a001..cb7fd89 100644
--- a/model/fw/green-yellow-red.cc
+++ b/model/fw/green-yellow-red.cc
@@ -64,8 +64,7 @@
 
 bool
 GreenYellowRed::DoPropagateInterest (Ptr<Face> inFace,
-                                     Ptr<const Interest> header,
-                                     Ptr<const Packet> origPacket,
+                                     Ptr<const Interest> interest,
                                      Ptr<pit::Entry> pitEntry)
 {
   NS_LOG_FUNCTION (this);
@@ -79,7 +78,7 @@
           metricFace.GetStatus () == fib::FaceMetric::NDN_FIB_YELLOW)
         break; //propagate only to green faces
 
-      if (!TrySendOutInterest (inFace, metricFace.GetFace (), header, origPacket, pitEntry))
+      if (!TrySendOutInterest (inFace, metricFace.GetFace (), interest, pitEntry))
         {
           continue;
         }
@@ -123,11 +122,10 @@
 void
 GreenYellowRed::DidReceiveValidNack (Ptr<Face> inFace,
                                      uint32_t nackCode,
-                                     Ptr<const Interest> header,
-                                     Ptr<const Packet> origPacket,
+                                     Ptr<const Interest> nack,
                                      Ptr<pit::Entry> pitEntry)
 {
-  super::DidReceiveValidNack (inFace, nackCode, header, origPacket, pitEntry);
+  super::DidReceiveValidNack (inFace, nackCode, nack, pitEntry);
 
   if (inFace != 0 &&
       (nackCode == Interest::NACK_CONGESTION ||