[REST] getutxos REST command (based on Bip64)

has parts of @mhearn #4351
* allows querying the utxos over REST
* same binary input and outputs as mentioned in Bip64
* input format = output format
* various rpc/rest regtests

src/rpcserver.cpp

@@ -992,7 +992,7 @@ void ServiceConnection(AcceptedConnection *conn)
 
         // Process via HTTP REST API
         } else if (strURI.substr(0, 6) == "/rest/" && GetBoolArg("-rest", false)) {
-            if (!HTTPReq_REST(conn, strURI, mapHeaders, fRun))
+            if (!HTTPReq_REST(conn, strURI, strRequest, mapHeaders, fRun))
                 break;
 
         } else {