Handle reference scripts in `UtxoState` and pretty-print them

[florentc]

This fixes the lack of pretty-printing for reference scripts in utxos.

Changes

• In Cooked.UtxoState, UtxoValueSet is renamed to UtxoPayloadSet and reference scripts are added to a now explicit UtxoPayload type.
• Generation of UtxoState in Cooked.Direct is adapted accordingly.
• Pretty-printing in Cooked.Pretty.Cooked also takes these changes into account and implement printing of reference script hash when applicable.