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/util/command-interest-validator.hpp b/src/util/command-interest-validator.hpp
index 6bd3250..2dcc947 100644
--- a/src/util/command-interest-validator.hpp
+++ b/src/util/command-interest-validator.hpp
@@ -17,6 +17,8 @@
 #include "../security/identity-certificate.hpp"
 #include "../security/sec-rule-specific.hpp"
 
+#include <list>
+
 namespace ndn {
 
 class CommandInterestValidator : public Validator