better loading indicators for timetables, talk and files

lib/widget/userAvatar.dart

@@ -60,11 +60,10 @@ class _UserAvatarState extends State<UserAvatar> {
 
   Future<_AvatarPayload?> _fetch(String url) async {
     try {
-      final auth = base64Encode(utf8.encode(AccountData().buildHttpAuthString()));
       final response = await http.get(
         Uri.parse(url),
         headers: {
-          'Authorization': 'Basic $auth',
+          'Authorization': AccountData().getBasicAuthHeader(),
           'Accept': 'image/png,image/jpeg,image/webp,image/svg+xml',
         },
       );