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/tools/ndnsec/list.hpp b/tools/ndnsec/list.hpp
index 90b4757..8a750f2 100644
--- a/tools/ndnsec/list.hpp
+++ b/tools/ndnsec/list.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2015 Regents of the University of California.
+ * Copyright (c) 2013-2016 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -40,7 +40,7 @@
   std::cout << certName << std::endl;
 
   if (verboseLevel >= 3) {
-    ndn::shared_ptr<ndn::IdentityCertificate> certificate = keyChain.getCertificate(certName);
+    ndn::shared_ptr<ndn::security::v1::IdentityCertificate> certificate = keyChain.getCertificate(certName);
     if (static_cast<bool>(certificate))
       certificate->printCertificate(std::cout, "            ");
   }