Operation for add-to-basket

Title: Operation for add-to-basket

Documentation:
The add-to-basket action has been moved inside an Operation. This means that it
has a pre- and post-trigger attached to it and workflows can be used.
To handle this the shop/add view has been added which calls the operation.

After the item is added the system will redirect based on a new configuration
switch in site.ini.
It is placed under the group ShopSettings and is called RedirectAfterAddToBasket.
It can contain on of these settings:
- basket - Redirect back to the basket to show the newly added item
- reload - Redirect back to where the user was previously, this allows
           the user to continue shopping.

The default is basket which redirects to the basket listing.