EST-260: fixing up creation of new bank mandates

1. Lease#newBankMandate now delegates to BankMandates#newBankMandate
2. in so doing, now correctly sets the landlord as the creditor

In addition:
- moved AgreementRole.Predicates.whetherCurrentIs to WithInterval.Predicates.whetherCurrentIs
- added FixedAssetRoles#findByParty
  - for possible (though unlikely) support of Party#assets contributed action/collection