Bases: django.core.management.base.NoArgsCommand
retreive relevant question updates for the user according to their subscriptions and recorded question views
src is a query set with questions or None dst - is an ordered dictionary update reporting cutoff time for each question to the latest value to be more permissive about updates
forms a subject line based on up to five most frequently used tags in the question_dict
question_dict is an instance of SortedDict, where questions are keys and values are meta_data accumulated during the question filtering