Implementing content store using Boost.MultiIndex container

Adding .SetGroupName("Ccnx") call to Ccnx-related objects (probably
missed some).  This call is advisory, but it is nice to give users
information about Ccnx-related objects (this information is accessible
via --PrintGroup=Ccnx command line argument)
diff --git a/model/ccnx-forwarding-strategy.cc b/model/ccnx-forwarding-strategy.cc
index 6d4b045..7159109 100644
--- a/model/ccnx-forwarding-strategy.cc
+++ b/model/ccnx-forwarding-strategy.cc
@@ -28,6 +28,7 @@
 TypeId CcnxForwardingStrategy::GetTypeId (void)
 {
   static TypeId tid = TypeId ("ns3::CcnxForwardingStrategy")
+    .SetGroupName ("Ccnx")
     .SetParent<Object> ()
   ;
   return tid;