Use timetable service in the applet, expand items to request more data

- Add expadedStateChanged() signal to departure items and connect it
to the applet to request additional data for the item
- Add data source name and index to DepartureInfo to identify the
item to update at the timetable service
- Fade in the route item if it was added later using the service
- Do not use "auto update" setting anymore in the applet, disable
polling (see last commit)
TODO: Remove setting completely and from the GUI