Consider pulling Batch InnerTransaction TX Hash generator into `RawTransactionWrapper`

[sappenin]

As of #654, the only place that the TxID/Hash of an inner Batch transaction is computed is inside of the binary codec (see here). However, we likely want to pull this out to be a @Derived field in the RawTransactionWrapper.java so that library users can more easily access that value if desired. This will look similar to SignedTransactionWrapper.hash().