added guardian letters with chat and multiple answer functionalities

lib/storage/modules_settings.g.dart

@@ -31,6 +31,7 @@ Map<String, dynamic> _$ModulesSettingsToJson(
 
 const _$ModulesEnumMap = {
   Modules.timetable: 'timetable',
+  Modules.parentLetters: 'parentLetters',
   Modules.ticker: 'ticker',
   Modules.talk: 'talk',
   Modules.files: 'files',

lib/storage/notification_settings.dart

@@ -16,9 +16,20 @@ class NotificationSettings {
   @JsonKey(defaultValue: false)
   bool talkPermissionPromptShown;
 
+  /// Same one-shot guards for the two occasions on which accounts with
+  /// parent letters are asked: right after signing in and, if the permission
+  /// is still missing, on the first visit of the parent letters.
+  @JsonKey(defaultValue: false)
+  bool guardianLoginPromptShown;
+
+  @JsonKey(defaultValue: false)
+  bool parentLettersPromptShown;
+
   NotificationSettings({
     this.enabled = true,
     this.talkPermissionPromptShown = false,
+    this.guardianLoginPromptShown = false,
+    this.parentLettersPromptShown = false,
   });
 
   factory NotificationSettings.fromJson(Map<String, dynamic> json) =>

lib/storage/notification_settings.g.dart

@@ -12,6 +12,8 @@ NotificationSettings _$NotificationSettingsFromJson(
   enabled: json['enabled'] as bool? ?? true,
   talkPermissionPromptShown:
       json['talkPermissionPromptShown'] as bool? ?? false,
+  guardianLoginPromptShown: json['guardianLoginPromptShown'] as bool? ?? false,
+  parentLettersPromptShown: json['parentLettersPromptShown'] as bool? ?? false,
 );
 
 Map<String, dynamic> _$NotificationSettingsToJson(
@@ -19,4 +21,6 @@ Map<String, dynamic> _$NotificationSettingsToJson(
 ) => <String, dynamic>{
   'enabled': instance.enabled,
   'talkPermissionPromptShown': instance.talkPermissionPromptShown,
+  'guardianLoginPromptShown': instance.guardianLoginPromptShown,
+  'parentLettersPromptShown': instance.parentLettersPromptShown,
 };