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/identity.hpp b/src/security/identity.hpp
index 0ac8201..1e4bd2c 100644
--- a/src/security/identity.hpp
+++ b/src/security/identity.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).
  *
@@ -116,7 +116,7 @@
    * @return the added key or existing key with the same key id.
    */
   Key
-  addKey(const PublicKey& publicKey, const name::Component& keyId = EMPTY_KEY_ID);
+  addKey(const v1::PublicKey& publicKey, const name::Component& keyId = EMPTY_KEY_ID);
 
   /**
    * @brief Remove a key.
@@ -147,7 +147,7 @@
    * @return the default key
    */
   Key&
-  setDefaultKey(const PublicKey& publicKey, const name::Component& keyId = EMPTY_KEY_ID);
+  setDefaultKey(const v1::PublicKey& publicKey, const name::Component& keyId = EMPTY_KEY_ID);
 
 NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PRIVATE:
   /**