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.cc b/model/cs/content-store-nocache.cc
index 8814c13..c5749e2 100644
--- a/model/cs/content-store-nocache.cc
+++ b/model/cs/content-store-nocache.cc
@@ -55,15 +55,15 @@
 {
 }
 
-boost::tuple<Ptr<Packet>, Ptr<const ContentObject>, Ptr<const Packet> >
+Ptr<ContentObject>
 Nocache::Lookup (Ptr<const Interest> interest)
 {
   this->m_cacheMissesTrace (interest);
-  return boost::tuple<Ptr<Packet>, Ptr<const ContentObject>, Ptr<const Packet> > (0, 0, 0);
+  return 0;
 }
 
 bool
-Nocache::Add (Ptr<const ContentObject> header, Ptr<const Packet> packet)
+Nocache::Add (Ptr<const ContentObject> data)
 {
   return false;
 }