Do not use ship address in UserAddress if it is not present on the order
Specify class_name for OptionValue's option_type association

If you attempted to assign any non Spree::OptionType object to this association, it would result in a vague uninitialized constant error
Showing line items on orders screen now when there are no shipments

Fixes #3958

Conflicts:
	backend/app/views/spree/admin/orders/_form.html.erb