data: add shortcuts to access SignatureType and KeyLocator

Also, modernize the API of SignatureInfo and deprecate
unsetKeyLocator() and unsetValidityPeriod()

Change-Id: I8b775a4deb185784a3dcc8bd96c8f5f0c2915854
diff --git a/tests/unit/security/pib/pib-impl.t.cpp b/tests/unit/security/pib/pib-impl.t.cpp
index 7b13306..24d2b86 100644
--- a/tests/unit/security/pib/pib-impl.t.cpp
+++ b/tests/unit/security/pib/pib-impl.t.cpp
@@ -331,8 +331,8 @@
   // Create a fake cert with the same name
   auto cert2 = this->id1Key2Cert1;
   cert2.setName(this->id1Key1Cert1.getName());
-  cert2.setSignatureInfo(this->id1Key2Cert1.getSignatureInfo());
-  cert2.setSignatureValue(this->id1Key2Cert1.getSignatureValue());
+  BOOST_CHECK_EQUAL(cert2.getSignatureInfo(), this->id1Key2Cert1.getSignatureInfo());
+  BOOST_CHECK_EQUAL(cert2.getSignatureValue(), this->id1Key2Cert1.getSignatureValue());
   this->pib.addCertificate(cert2);
 
   auto cert3 = this->pib.getCertificate(this->id1Key1Cert1.getName());