Fixed saved view model, slightly changed sorting dialog, fixed open document in system viewer not working because file has folder-like structure.

lib/core/translation/sort_field_localization_mapper.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/material.dart';
+import 'package:paperless_api/paperless_api.dart';
+import 'package:paperless_mobile/generated/l10n.dart';
+
+String translateSortField(BuildContext context, SortField sortField) {
+  switch (sortField) {
+    case SortField.archiveSerialNumber:
+      return S.of(context).documentArchiveSerialNumberPropertyShortLabel;
+    case SortField.correspondentName:
+      return S.of(context).documentCorrespondentPropertyLabel;
+    case SortField.title:
+      return S.of(context).documentTitlePropertyLabel;
+    case SortField.documentType:
+      return S.of(context).documentDocumentTypePropertyLabel;
+    case SortField.created:
+      return S.of(context).documentCreatedPropertyLabel;
+    case SortField.added:
+      return S.of(context).documentAddedPropertyLabel;
+    case SortField.modified:
+      return S.of(context).documentModifiedPropertyLabel;
+  }
+}