Move logic for creating a new payment processor from CRM_Admin_Form_PaymentProcessor::updatePaymentProcessor to BAO

Unit tests are failing because they're calling CRM_Financial_BAO_PaymentProcessor::create and expecting it to create the entity_financial_account row when financial_account_id is passed in. However the logic for this is still in CRM_Admin_Form_PaymentProcessor::updatePaymentProcessor.

Please move necessary logic from the form to the BAO, and have the form postProcess call the BAO. Then I can go in and fix the tests.