Add cascading deletes

[seanrockster]

You might recall me having an issue with multiple unfinalized carts. I'm writing a task to delete them but, alas, there are multiple foreign constrains that are prevent me automating this. It would be great if a delete could cascade so if i delete an order, it deletes frozen prices, and order properties, and order line properties and order lines etc etc etc.

Thanks.

[mattbrailsford]

I'm not sure what code you are using, but we already do this