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/cs/content-store-nocache.h b/model/cs/content-store-nocache.h
index 6d38f40..79d1284 100644
--- a/model/cs/content-store-nocache.h
+++ b/model/cs/content-store-nocache.h
@@ -54,11 +54,11 @@
   virtual
   ~Nocache ();
 
-  virtual boost::tuple<Ptr<Packet>, Ptr<const ContentObject>, Ptr<const Packet> >
+  virtual Ptr<ContentObject>
   Lookup (Ptr<const Interest> interest);
 
   virtual bool
-  Add (Ptr<const ContentObject> header, Ptr<const Packet> packet);
+  Add (Ptr<const ContentObject> data);
 
   virtual void
   Print (std::ostream &os) const;