added guardian login with views for their assigned childs

lib/widget/file_viewer/unknown_preview_block.dart

@@ -1,8 +1,8 @@
 import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/material.dart';
 
-import '../../model/account_data.dart';
 import '../../model/endpoint_data.dart';
+import '../../session/session_manager.dart';
 import '../../share_intent/remote_file_ref.dart';
 import '../app_progress_indicator.dart';
 
@@ -67,7 +67,7 @@ class _UnknownPreviewBlockState extends State<UnknownPreviewBlock> {
       width: _previewSize,
       height: _previewSize,
       child: CachedNetworkImage(
-        httpHeaders: AccountData().authHeaders(),
+        httpHeaders: SessionManager().requireNextcloud().authHeaders,
         imageUrl: _ncPreviewUrl(remote, width: 360),
         fadeInDuration: Duration.zero,
         fadeOutDuration: Duration.zero,