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/face.cpp b/src/face.cpp
index fbaee26..bbb9f08 100644
--- a/src/face.cpp
+++ b/src/face.cpp
@@ -321,7 +321,7 @@
                         const OnInterest& onInterest,
                         const RegisterPrefixSuccessCallback& onSuccess,
                         const RegisterPrefixFailureCallback& onFailure,
-                        const IdentityCertificate& certificate,
+                        const security::v1::IdentityCertificate& certificate,
                         uint64_t flags)
 {
   security::SigningInfo signingInfo;
@@ -335,7 +335,7 @@
 Face::setInterestFilter(const InterestFilter& interestFilter,
                         const OnInterest& onInterest,
                         const RegisterPrefixFailureCallback& onFailure,
-                        const IdentityCertificate& certificate,
+                        const security::v1::IdentityCertificate& certificate,
                         uint64_t flags)
 {
   security::SigningInfo signingInfo;
@@ -390,7 +390,7 @@
 Face::registerPrefix(const Name& prefix,
                      const RegisterPrefixSuccessCallback& onSuccess,
                      const RegisterPrefixFailureCallback& onFailure,
-                     const IdentityCertificate& certificate,
+                     const security::v1::IdentityCertificate& certificate,
                      uint64_t flags)
 {
   security::SigningInfo signingInfo;