message: make tokentransfer builder optionally take a tx signer instead of a private key
diff: @@ -1086,7 +1086,7 @@ function makeTokenTransfer(recipientAddress: string, tokenType: string,
  recipientAddress, consensusHash, tokenType, tokenAmount, scratchArea))
  return senderKey.getAddress().then(
  - (senderAddress) => {
  + (senderAddress) =>
  Promise.all([network.getUTXOs(senderAddress), network.getFeeRate(), txPromise])
  .then(([utxos, feeRate, tokenTransferTX]) => {
  const txB = bitcoinjs.TransactionBuilder.fromTransaction(tokenTransferTX, network.layer1)
  