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);
+}

lib/storage/timetable/timetableSettings.g.dart

@@ -0,0 +1,17 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'timetableSettings.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+TimetableSettings _$TimetableSettingsFromJson(Map<String, dynamic> json) =>
+    TimetableSettings(
+      zoom: (json['zoom'] as num).toDouble(),
+    );
+
+Map<String, dynamic> _$TimetableSettingsToJson(TimetableSettings instance) =>
+    <String, dynamic>{
+      'zoom': instance.zoom,
+    };