feat(transport_helper): add fromJson constructor for Departure class

lib/transport_helper.dart

@@ -739,7 +739,6 @@ class Line {
   }
 }
 
-// TODO: add fromJson
 class Departure {
   static const String tableName = "departure";
 
@@ -772,6 +771,18 @@ class Departure {
       departureTime: map["departuretime"] as DateTime,
     );
   }
+  factory Departure.fromJson(Map<String, dynamic> json) {
+    Vehicle vehicle = Vehicle.fromJson(json["Product"]);
+    vehicle.dbInsert();
+    Station station = Station.fromJson(json["stop"]);
+    station.dbInsert();
+    return Departure(
+      vehicleId: vehicle.id,
+      stationId: station.id,
+      departureTime: json["time"],
+    );
+  }
+
   static void initDepartureTable() async {
     Database database = DbHelper.db;
     String vehicle = Vehicle.tableName;