add normalized hash for Txs


This add  .calcNormalizedHash and .getNormalizedHash, (as the existing .calcHash and getHash) for
the normalized TXID (NTXID) as implemented in: 
https://github.com/bitcoin/bitcoin/pull/3656

Some NTXID use cases are:
 - identifying transaction "clones" due to tx malleability
 - identifying incomplete TXs, for multisig