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/tests/test-data.cpp b/tests/test-data.cpp
index 2e022a1..bfb2cd4 100644
--- a/tests/test-data.cpp
+++ b/tests/test-data.cpp
@@ -13,6 +13,7 @@
 #include "data.hpp"
 #include "security/key-chain.hpp"
 #include "security/cryptopp.hpp"
+#include "encoding/buffer-stream.hpp"
 
 #include "boost-test.hpp"