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.h b/model/fw/green-yellow-red.h
index 1c4dcde..11817bf 100644
--- a/model/fw/green-yellow-red.h
+++ b/model/fw/green-yellow-red.h
@@ -44,8 +44,7 @@
 
   virtual bool
   DoPropagateInterest (Ptr<Face> inFace,
-                       Ptr<const Interest> header,
-                       Ptr<const Packet> origPacket,
+                       Ptr<const Interest> interest,
                        Ptr<pit::Entry> pitEntry);
 
   virtual void
@@ -54,8 +53,7 @@
   virtual void
   DidReceiveValidNack (Ptr<Face> incomingFace,
                        uint32_t nackCode,
-                       Ptr<const Interest> header,
-                       Ptr<const Packet> origPacket,
+                       Ptr<const Interest> nack,
                        Ptr<pit::Entry> pitEntry);
 private:
   typedef Nacks super;