feat(departures): make some adaptations to supp diff departure srces

with these adaptations to the api_handler and Departure.fromJson,
the fromJson-factory now works for responses from both /departureBoard
and /tripDetail

for /tripDetail a little json-copying is used, see
ApiHandler._expandDeparturesJson

lib/main.dart

@@ -348,7 +348,7 @@ class _ChooseArrivalPageState extends State<ChooseArrivalPage> {
             Expanded(
               child: SizedBox(
                 height: 400,
-                child: DepartureList(
+                child: ArrivalList(
                   departureList: departureList,
                   onTapped: _handleArrivalTapped,
                 ),
@@ -398,11 +398,11 @@ class ArrivalList extends StatelessWidget {
       children: [
         for (Departure departure in departureList)
           ListTile(
-            title: Text(departure.stationId),
+            title: Text(departure.stationName),
             subtitle: Text(departure.arrivalTime.toString()),
             onTap: () => onTapped(departure),
           ),
       ],
     );
   }
-}
+}