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/core/time.cpp b/daemon/core/time.cpp
index 712779d..c216df4 100644
--- a/daemon/core/time.cpp
+++ b/daemon/core/time.cpp
@@ -9,7 +9,7 @@
 #include <stdexcept>
 #include <sys/time.h>
 
-namespace ndn {
+namespace nfd {
 namespace time {
 
 Point
@@ -42,4 +42,4 @@
 }
 
 } // namespace time
-} // namespace ndn
+} // namespace nfd