src: Changing namespace ndn to namespace nfd

Also, this commit imports used classes from ::ndn namespace (from
NDN-CPP library) directly to ::nfd namespace.

refs: #1163

Change-Id: I9cc9d72e00af495b4ed0c84e6d418a7c9ba986cb
diff --git a/daemon/face/face.cpp b/daemon/face/face.cpp
index 1aa5184..6518117 100644
--- a/daemon/face/face.cpp
+++ b/daemon/face/face.cpp
@@ -6,7 +6,7 @@
 
 #include "face.hpp"
 
-namespace ndn {
+namespace nfd {
 
 Face::Face(FaceId id)
   : m_id(id)
@@ -49,4 +49,4 @@
 }
 
 
-} //namespace ndn
+} //namespace nfd