src: Refactoring common.hpp and minimizing exposed includes

Face class has relatively large rewrite to hide internals using
Implementor pattern.  As of this commit, <boost/asio.hpp> is not
automatically included whenever ndn-cxx/face.hpp is included.  If it is
needed to directly work with io_service, asio.hpp should be specifically
included.

Change-Id: Ie742b851025b4e3da634eb981319df0f42937855
diff --git a/src/name-component.hpp b/src/name-component.hpp
index b83dd40..d58e4d6 100644
--- a/src/name-component.hpp
+++ b/src/name-component.hpp
@@ -19,6 +19,7 @@
 
 #include "common.hpp"
 #include "encoding/block.hpp"
+#include "encoding/block-helpers.hpp"
 #include "encoding/encoding-buffer.hpp"
 #include "util/string-helper.hpp"