Change authentication method; Add invoice<->packing slips; Add location and category information to invoice; Add new invoice status "Vendor Denied"

1. Add authentication method right after "parse packing slip" to improve the performance.
2. Add packing slip information to related invoice.
3. Add location and category information to invoice. Extra columns on Openerp side
4. Add new invoice status "Vendor Denied". This state is identical with the "draft" state.