security: Reorganizing source code to prepare for support of two version of NDN certificates

This commit also removes unused ndn_digestSha256 function and deprecates
crypto::sha256 in favor of crypto::computeSha256Digest in util/crypto.hpp.

Change-Id: I24ee50ff073a96b868633bdf2cfade412d3605f3
Refs: #3098
diff --git a/src/security/command-interest-validator.cpp b/src/security/command-interest-validator.cpp
index ddba90e..f877f41 100644
--- a/src/security/command-interest-validator.cpp
+++ b/src/security/command-interest-validator.cpp
@@ -20,7 +20,7 @@
  */
 
 #include "command-interest-validator.hpp"
-#include "identity-certificate.hpp"
+#include "v1/identity-certificate.hpp"
 #include <boost/lexical_cast.hpp>
 
 namespace ndn {
@@ -146,9 +146,9 @@
   }
 
   try {
-    keyName = IdentityCertificate::certificateNameToPublicKeyName(keyLocator.getName());
+    keyName = v1::IdentityCertificate::certificateNameToPublicKeyName(keyLocator.getName());
   }
-  catch (const IdentityCertificate::Error&) {
+  catch (const v1::IdentityCertificate::Error&) {
     return ErrorCode::BAD_CERT_NAME;
   }