security: Fixing compilation errors and providing backward compatible interface for Signature*

This commit includes missed includes and "re-introduction" of
setKeyLocator method into Signature interface.  This method was used in
dependent applications as part of SignatureSha256With(Rsa|Ecdsa) data
structures.

Change-Id: I788f687600bb2729ea8265e23d4a31b990b8ed96
Refs: #1750, #1755
diff --git a/src/signature.hpp b/src/signature.hpp
index d6dd730..66a3f52 100644
--- a/src/signature.hpp
+++ b/src/signature.hpp
@@ -22,6 +22,7 @@
 #ifndef NDN_SIGNATURE_HPP
 #define NDN_SIGNATURE_HPP
 
+#include "common.hpp"
 #include "signature-info.hpp"
 
 namespace ndn {
@@ -122,6 +123,12 @@
     return m_info.getKeyLocator();
   }
 
+  /// @brief Set KeyLocator
+  void
+  setKeyLocator(const KeyLocator& keyLocator)
+  {
+    m_info.setKeyLocator(keyLocator);
+  }
 
 public: // EqualityComparable concept
   bool