Add CPubKey m_public_key to Poll class and serialize for payload v3

Note this is for future use.

src/gridcoin/voting/payloads.h

@@ -170,10 +170,11 @@ class PollPayload : public IContractPayload
         READWRITE(m_version);
         READWRITE(m_poll);
 
-        // The poll m_additional_fields is serialized here rather than in the poll class, because it depends on the
-        // payload version.
+        // The poll m_additional_fields and m_public_key are serialized here rather than in the poll class, because they
+        // depend on the payload version.
         if (m_version >= 3) {
             READWRITE(m_poll.m_additional_fields);
+            READWRITE(m_poll.m_public_key);
         }
 
         READWRITE(m_claim);

src/gridcoin/voting/poll.h

@@ -9,6 +9,7 @@
 #include "gridcoin/voting/fwd.h"
 #include "serialize.h"
 #include "uint256.h"
+#include "pubkey.h"
 
 #include <string>
 #include <vector>
@@ -390,6 +391,7 @@ class Poll
     std::string m_question;                  //!< UTF-8 prompt that voters shall answer.
     ChoiceList m_choices;                    //!< The set of possible answers to the poll.
     AdditionalFieldList m_additional_fields; //!< The set of additional fields for the poll.
+    CPubKey m_public_key;                    //!< Public key of the project.
 
     // Memory only:
     int64_t m_timestamp;          //!< Time of the poll's containing transaction.
@@ -558,8 +560,8 @@ class Poll
             READWRITE(m_choices);
         }
 
-        // Note that m_additional_fields is not serialized here, but rather in the PollPayload class. This
-        // is because it depends on the poll payload version, which is not available here.
+        // Note that m_additional_fields and m_public_key are not serialized here, but rather in the PollPayload class. This
+        // is because they depend on the poll payload version, which is not available here.
     }
 }; // Poll
 } // namespace GRC