Resolve "Use ApplicationSettings widgets from flutter_custom_toolbox"

Closes #88 (closed)

lib/cubit/theme_cubit.dart

-import 'package:flutter_custom_toolbox/flutter_toolbox.dart';
-import 'package:flutter/material.dart';
-
-part 'theme_state.dart';
-
-class ThemeCubit extends HydratedCubit<ThemeModeState> {
-  ThemeCubit() : super(const ThemeModeState());
-
-  void getTheme(ThemeModeState state) {
-    emit(state);
-  }
-
-  @override
-  ThemeModeState? fromJson(Map<String, dynamic> json) {
-    switch (json['themeMode']) {
-      case 'ThemeMode.dark':
-        return const ThemeModeState(themeMode: ThemeMode.dark);
-      case 'ThemeMode.light':
-        return const ThemeModeState(themeMode: ThemeMode.light);
-      case 'ThemeMode.system':
-      default:
-        return const ThemeModeState(themeMode: ThemeMode.system);
-    }
-  }
-
-  @override
-  Map<String, String>? toJson(ThemeModeState state) {
-    return <String, String>{'themeMode': state.themeMode.toString()};
-  }
-}