On openerp client side:
1. Fix button "create draft invoice".
2. rewrite price calculation method.
3. Add Group check-box to create invoice based on multiple packing slips.
4. Define new status of invoice: draft, Septa Manager Approved, Vendor Approved, Paid.
5. Add function to handle invoice processing.

On Vendor client side:
1. Display invoices that are in "Septa Manager Approved" and "Vendor Approved" status.
2. Add to option button for vendor, "Approve" and "Deny"
Handling invoice display and processing