initial version of DPIC6 that is compatible with new Moo-based cart
now working with test app but still some debug work to do
change items to products in checkout route
added login failed error to get login
reduce _cart_load calls from 3 to 1 in cart route
guest->authorised transition: fix combining products
new 'improved' guest->authorized saved cart item loader
added optiont to use return_url after login success
cruft cleanup
remove some Dumper calls that are no longer needed