better loading indicators for timetables, talk and files

lib/view/pages/talk/components/chatMessage.dart

@@ -63,7 +63,8 @@ class ChatMessage {
               fadeInDuration: Duration.zero,
               fadeOutDuration: Duration.zero,
               errorListener: (value) {},
-              imageUrl: 'https://${AccountData().buildHttpAuthString()}@${EndpointData().nextcloud().full()}/index.php/core/preview?fileId=${file!.id}&x=130&y=-1&a=1',
+              httpHeaders: AccountData().authHeaders(),
+              imageUrl: 'https://${EndpointData().nextcloud().full()}/index.php/core/preview?fileId=${file!.id}&x=130&y=-1&a=1',
             ),
             if(originalMessage != '{file}') ...[
               SizedBox(height: 5),