Fixes #58
The buttons were not displayed because of an exception in the GetAttributes method from the ProductAttributeService.
I fixed that code to handle the case where Attributes have been deleted.
I also added code to the ProductAttributesPartDriver, so that when the Part is saved, any deleted attributes are removed from the record.
The change I had to make to the validation makes it so that the record for the ProductAttributesPart is also updated whenever someone tries to add the product to the cart.
Fixes #58 The buttons were not displayed because of an exception in the GetAttributes method from the ProductAttributeService.
I fixed that code to handle the case where Attributes have been deleted. I also added code to the ProductAttributesPartDriver, so that when the Part is saved, any deleted attributes are removed from the record.