Enhancement to function edd_get_payment_meta_cart_details

Add some information about the associated bundle to the child products in the cart details. 

This is necessary to know for example which was the price option picked for a given download when we want a custom site count / expiration date for licensing.

Related support forum thread: https://easydigitaldownloads.com/support/topic/bundles-variable-pricing-custom-expirationsite-count/