py-braintree: updated to 4.18.0

4.18.0

Replace nose usage for tests with unittest (Thanks @arthurzam)
Remove mock dev dependency (Thanks @arthurzam)
Add ExcessiveRetry to GatewayRejectionReason
Add pre_dispute_program to Dispute and DisputeSearch
Add AutoAccepted status to Dispute
Add DisputeAutoAccepted to WebhookNotification.Kind
Deprecate chargeback_protection_level and add protection_level to Dispute and DisputeSearch
Add shipping object to submit_for_settlement_signature
Add SEPADirectDebitAccount payment method
Add SEPADirectDebitAccount to transaction object
Add SEPA_DIRECT_DEBIT_ACCOUNT to PaymentInstrumentType
Add sepa_debit_paypal_v2_order_id to TransactionSearch
Add sepa_direct_debit_accounts to Customer
Add SEPA Direct Debit specific error codes

(adam)