OpenERP7: POS Enhancements

Adding more features to openERP V7 point of sale including:
- Keyboard shortcuts for non-touch monitors.
- One key press to finish an order in cash.
- Apply fixed discount for product or the whole order.
- Apply percentage discount for product or the whole order.
- One click to void an order.
- Increase, decrease and edit product Qty.
- Easily remove one product from the order with Delete key.
- Add a different logo, address, phone, exchange/return policy for each shop.
- Logo will appear on POS receipt.

* Discounts will appear in the POS back end orders page.
* Discounts reflected correctly into accounting module.