- timezone data is imported from SQLite DB from Thunderbird Lighting 1.0pre
- contains iCal VTIMEZONE component
- also contains not yet used latitude and longitude for timezone
- methods to convert between TZID string, nummeric tz_id and VTIMEZONE
iCal component
--> preparation to store timezone information for each events
(using tz_id as foreing key into egw_cal_timezones table)