We add a Token class to Tx, which adds an easy to use API when compared
to the plain iterator. The main point of the API chosen is to make sure
we don't do unneeded parsing or copying for tokens unless needed.
Additionally refactor the ValidationPrivate::UnspentOutput class to
inherit from the Tx::Output class in order to avoid lots of duplicated
logic on handling the data.
tomFlowee
ced4f98beb