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/sec-tpm.hpp b/src/security/sec-tpm.hpp
index 1ade1d6..3da278e 100644
--- a/src/security/sec-tpm.hpp
+++ b/src/security/sec-tpm.hpp
@@ -28,10 +28,11 @@
 #include "security-common.hpp"
 #include "../name.hpp"
 #include "../data.hpp"
-#include "public-key.hpp"
 #include "key-params.hpp"
+#include "v1/public-key.hpp"
 
 namespace ndn {
+namespace security {
 
 /**
  * @brief SecTpm is the base class of the TPM classes.
@@ -136,7 +137,7 @@
    * @return The public key.
    * @throws SecTpm::Error if public key does not exist in TPM.
    */
-  virtual shared_ptr<PublicKey>
+  virtual shared_ptr<v1::PublicKey>
   getPublicKeyFromTpm(const Name& keyName) = 0;
 
   /**
@@ -300,6 +301,10 @@
   std::string m_location;
 };
 
+} // namespace security
+
+using security::SecTpm;
+
 } // namespace ndn
 
 #endif // NDN_SECURITY_SEC_TPM_HPP