Base transaction ID for financial institutes

Adds transaction id to invoice and sale models and views. On Sales order, you can specify the transaction ID used for the payment and it will be propagated to the invoice (even if made from packing). This is mostly used for e-commerce handling. You can then add a mapping on that SO field to save the e-commerce financial Transaction ID into the OpenERP SO field. The main purpose is to ease the reconciliation process and be able to find the partner when importing the bank statement.