Made GradeAverage persistent

lib/storage/base/settings.dart

@@ -0,0 +1,30 @@
+import 'package:flutter/material.dart';
+import 'package:json_annotation/json_annotation.dart';
+
+import '../gradeAverages/gradeAveragesSettings.dart';
+
+part 'settings.g.dart';
+
+@JsonSerializable(explicitToJson: true)
+class Settings {
+  @JsonKey(
+    toJson: _themeToJson,
+    fromJson: _themeFromJson,
+  )
+  ThemeMode appTheme;
+  bool devToolsEnabled;
+
+  GradeAveragesSettings gradeAveragesSettings;
+
+  Settings({
+    required this.appTheme,
+    required this.devToolsEnabled,
+    required this.gradeAveragesSettings
+  });
+
+  static String _themeToJson(ThemeMode m) => m.name;
+  static ThemeMode _themeFromJson(String m) => ThemeMode.values.firstWhere((element) => element.name == m);
+
+  factory Settings.fromJson(Map<String, dynamic> json) => _$SettingsFromJson(json);
+  Map<String, dynamic> toJson() => _$SettingsToJson(this);
+}