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-net-device-face.cc b/model/ccnx-net-device-face.cc
index b5816a4..9bdcd43 100644
--- a/model/ccnx-net-device-face.cc
+++ b/model/ccnx-net-device-face.cc
@@ -38,6 +38,7 @@
 CcnxNetDeviceFace::GetTypeId ()
 {
   static TypeId tid = TypeId ("ns3::CcnxNetDeviceFace")
+    .SetGroupName ("Ccnx")
     .SetParent<CcnxFace> ()
   ;
   return tid;