Squashed commit of the following:

commit 73aa995a60205ed0c53f8c46104f69ee4505f7e7
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Thu Jul 24 11:30:33 2014 +0100

    Update shopping cart so that you can add discounts via a specific URL (without needing a form)

commit c63d3d7aeaa7cdd0f65d3b7d1a211d5104d19512
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Tue Jul 22 11:24:11 2014 +0100

    Hide discounts divider if we do not want to see any discount info

commit 94cdadf495659d325a1f2e3eb3f7384a5bd5e646
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Tue Jul 22 11:21:53 2014 +0100

    Add ability to hide discounts and discount form

commit 870df2b8097be25d9cf9bccbb3222087677f1081
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Tue Jul 22 11:12:49 2014 +0100

    Add support for a member being added to a group with a discount code

commit 4ff7ef93e91811db877dd08b7a780ee8c341cffb
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Mon Jul 21 21:40:20 2014 +0100

    Update shopping cart to accept discounts with no expirey date

commit 8f1894997dc3167b8e9effcb34b9c05d313f1caa
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Mon Jul 21 20:49:06 2014 +0100

    Clean up shopping cart process to retain discounts when emptied

commit 7cda7225ea65d9b796d89ddd08e35604a0b8ec7c
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Mon Jul 21 20:40:12 2014 +0100

    Add tracking of a discount to an order

commit 7a634290f6f5288cca75609a206e31a25ccfb17f
Author: Morven Lewis-Everley <morven@i-lateral.com>
Date:   Mon Jul 21 18:09:52 2014 +0100

    Add basic discount codes and support too shopping cart for discounts