Add PubKeyDestination for P2PK scripts

P2PK scripts are not PKHash destinations, they should have their own
type.

This also results in no longer showing a p2pkh address for p2pk outputs.
However for backwards compatibility, ListCoinst will still do this
conversion.

src/rpc/util.cpp

@@ -253,6 +253,11 @@ public:
         return UniValue(UniValue::VOBJ);
     }
 
+    UniValue operator()(const PubKeyDestination& dest) const
+    {
+        return UniValue(UniValue::VOBJ);
+    }
+
     UniValue operator()(const PKHash& keyID) const
     {
         UniValue obj(UniValue::VOBJ);