Made timetable zoom persistent

lib/storage/timetable/timetableSettings.dart

@@ -0,0 +1,13 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'timetableSettings.g.dart';
+
+@JsonSerializable()
+class TimetableSettings {
+  double zoom;
+
+  TimetableSettings({required this.zoom});
+
+  factory TimetableSettings.fromJson(Map<String, dynamic> json) => _$TimetableSettingsFromJson(json);
+  Map<String, dynamic> toJson() => _$TimetableSettingsToJson(this);
+}