Support for Conway certificate types

[agaffney]

Multiple certificate types were added in Conway

; DELEG
reg_cert = (7, stake_credential, coin)
unreg_cert = (8, stake_credential, coin)
vote_deleg_cert = (9, stake_credential, drep)
stake_vote_deleg_cert = (10, stake_credential, pool_keyhash, drep)
stake_reg_deleg_cert = (11, stake_credential, pool_keyhash, coin)
vote_reg_deleg_cert = (12, stake_credential, drep, coin)
stake_vote_reg_deleg_cert = (13, stake_credential, pool_keyhash, drep, coin)

; GOVCERT
auth_committee_hot_cert = (14, committee_cold_credential, committee_hot_credential)
resign_committee_cold_cert = (15, committee_cold_credential, anchor / null)
reg_drep_cert = (16, drep_credential, coin, anchor / null)
unreg_drep_cert = (17, drep_credential, coin)
update_drep_cert = (18, drep_credential, anchor / null)