Add Tx parsing feature

[uhbif19]

Parser would probably look like parseTx :: CEMScriptCompiled script => TxBody -> CEMScriptDatum script, where type CEMScriptDatum script = (Params script, State script). Though TxBody from cardano-api might be actually inconvenient for specific indexer interface (#44). But they are nice to have to do roundtrip tests in PSM backend, as it uses cardano-api types.

There should be existent implementation somewhere in old hydra-aucton.

TODO:

• Add parsing function
• Basic build-parse roundtrip test
• Use it in state-machine tests (to check it always works and created Tx are always correct)

[uhbif19]

FYI @euonymos , signature you asked for