security: Add v2::Validator implementation

Based on the code originally written by Qiuhan Ding

Change-Id: Ib66e24f49d0b6fb2ae21ea1fca7b9ec62ecb753a
Refs: #3289, #1872
diff --git a/src/security/v2/key-chain.hpp b/src/security/v2/key-chain.hpp
index 0e8402e..7cb71f2 100644
--- a/src/security/v2/key-chain.hpp
+++ b/src/security/v2/key-chain.hpp
@@ -22,6 +22,7 @@
 #ifndef NDN_SECURITY_V2_KEY_CHAIN_HPP
 #define NDN_SECURITY_V2_KEY_CHAIN_HPP
 
+#include "../security-common.hpp"
 #include "certificate.hpp"
 #include "../key-params.hpp"
 #include "../pib/pib.hpp"