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/flooding.h b/model/fw/flooding.h
index 5eadabb..f7ce55a 100644
--- a/model/fw/flooding.h
+++ b/model/fw/flooding.h
@@ -60,8 +60,7 @@
   // inherited from  Nacks/ForwardingStrategy
   virtual bool
   DoPropagateInterest (Ptr<Face> inFace,
-                       Ptr<const Interest> header,
-                       Ptr<const Packet> origPacket,
+                       Ptr<const Interest> interest,
                        Ptr<pit::Entry> pitEntry);
 
 protected: