API refactoring. ren default_start_dt -> default_start, default_end_dt -> default_end, rm default_start_DT, default_end_DT, deprecate, reorder functions in base module
renamed:         - cal_to_strftime_wkday -> wkday_to_mon1,
        - strftime_to_cal_wkday -> wkday_to_mon0. removed: - first_weekday_sun0.
update to changed API
remove default_tzinfo
Merge branch 'master' of git://github.com/plone/plone.app.event