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/security/public-key.cpp b/src/security/public-key.cpp
index 17f204b..9977950 100644
--- a/src/security/public-key.cpp
+++ b/src/security/public-key.cpp
@@ -13,8 +13,9 @@
  * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
  */
 
-#include "common.hpp"
 #include "public-key.hpp"
+
+#include "../encoding/oid.hpp"
 #include "cryptopp.hpp"
 
 using namespace std;