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.cpp b/src/security/v2/key-chain.cpp
index 850ad58..47cb75d 100644
--- a/src/security/v2/key-chain.cpp
+++ b/src/security/v2/key-chain.cpp
@@ -681,6 +681,8 @@
 
   sigInfo.setSignatureType(getSignatureType(key.getKeyType(), params.getDigestAlgorithm()));
   sigInfo.setKeyLocator(KeyLocator(key.getName()));
+
+  NDN_LOG_TRACE("Prepared signature info: " << sigInfo);
   return std::make_tuple(key.getName(), sigInfo);
 }