'Call to generate specific instructions for each item in the order.  This gets displayed on the receipt
page, typically.  Instructions are something like "visit your dashboard to see your new courses".
This will return two things in a pair.  The first will be a dict with keys=OrderItemSubclassPK corresponding
to an OrderItem and values=a set of html instructions they generate.  The second will be a set of de-duped
html instructions'

def generate_receipt_instructions(self):

    instruction_set = set([])
    instruction_dict = {}
    order_items = OrderItem.objects.filter(order=self).select_subclasses()
    for item in order_items:
        (item_pk_with_subclass, set_of_html) = item.generate_receipt_instructions()
        instruction_dict[item_pk_with_subclass] = set_of_html
        instruction_set.update(set_of_html)
    return (instruction_dict, instruction_set)
