clean recipient_case_match_property in reminders form
clean recipient_case_match_type in reminders form
clean case_match_value in reminders form
general clean method is unnecessary since the values are cleaned separately in reminders form
clean schedule_length in reminders form
clean max iteration count in reminders form
clean until in reminders form
since the value for callback intervals in reminders is stored as a list but edited as a string, flatten it here
set reminder_handler.events to a list of  CaseReminderEvents not dicts
finish saving reminder handler
add choices to max_question_retries