Account invoice sequence fix

This module should be used by anyone who has initiated an OpenERP with spanish localization modules 
did not install the module "nan_account_invoice_sequence", and has already accepted several invoices.
In this circumstance, once the module "nan_account_invoice_sequence" is installed the invoices already created 
will loose the invoice number, because it was the move number and the nan module adds a separate field to store the 
invoice number.
  
What this module will do i wizard will do is select all invoices with moves and copy the move number to the new invoice number field.
This wizard should be run just after module "nan_account_invoice_sequence" has been installed, and no new invoices have been produced in the system.
It is highly recommended that once the wizard has been run, the module should be removed, so as to avoid any furter use that might overwrite the existing invoice numbers.