Save trxn_id, payment_method_id and check_number to both contribution and financial_trxn tables

When editing a contribution, the check number, Payment Method, and Transaction ID fields are correctly being stored in civicrm_contribution pending implementation post 4.3 of partial payments. However, in 4.3 these values should also be stored in civicrm_financial_trxn. When partial payments is implemented, these fields will be dropped from civicrm_contribution.