Formalise a way to retrieve and update course section start and end dates at course format API level

In analytics we are interested in retrieving section end dates and update them, we are currently doing it using get_section_dates and update_end_date, which is specific to format_weeks; this is not ideal because we are using the method_exists trick, an API should communicate with other APIs with methods available at base class level and a format_months extending format_base should also work in analytics (although if that format would exist it would probably extend format_weeks).This case is a bit on the border because not all formats have sections.