io utils; single favorite folder exporting and importing

lib/pages/favorites/favorite_actions.dart

@@ -27,10 +27,26 @@ Future<void> newFolder() async {
                       });
                     }
                   },
-                )
+                ),
               ],
             ).paddingHorizontal(16),
             actions: [
+              TextButton(
+                child: Text("Import from file".tl),
+                onPressed: () async {
+                  var file = await selectFile(ext: ['json']);
+                  if(file == null) return;
+                  var data = await file.readAsBytes();
+                  try {
+                    LocalFavoritesManager().fromJson(utf8.decode(data));
+                  }
+                  catch(e) {
+                    context.showMessage(message: "Failed to import".tl);
+                    return;
+                  }
+                  context.pop();
+                },
+              ).paddingRight(4),
               FilledButton(
                 onPressed: () {
                   var e = validateFolderName(controller.text);

lib/pages/favorites/favorites_page.dart

@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'dart:math';
 
 import 'package:flutter/material.dart';
@@ -9,6 +10,7 @@ import 'package:venera/foundation/comic_source/comic_source.dart';
 import 'package:venera/foundation/comic_type.dart';
 import 'package:venera/foundation/favorites.dart';
 import 'package:venera/foundation/res.dart';
+import 'package:venera/utils/io.dart';
 import 'package:venera/utils/translations.dart';
 
 part 'favorite_actions.dart';
@@ -134,7 +136,12 @@ class _FavoritesPageState extends State<FavoritesPage>  {
                     )
                   : null,
             ),
-            title: Text("Unselected".tl),
+            title: GestureDetector(
+              onTap: context.width < _kTwoPanelChangeWidth
+                  ? showFolderSelector
+                  : null,
+              child: Text("Unselected".tl),
+            ),
           ),
         ],
       );

lib/pages/favorites/local_favorites_page.dart

@@ -15,8 +15,10 @@ class _LocalFavoritesPageState extends State<_LocalFavoritesPage> {
   late List<FavoriteItem> comics;
 
   void updateComics() {
+    print(comics.length);
     setState(() {
       comics = LocalFavoritesManager().getAllComics(widget.folder);
+      print(comics.length);
     });
   }
 
@@ -64,7 +66,6 @@ class _LocalFavoritesPageState extends State<_LocalFavoritesPage> {
                           favPage.setFolder(false, null);
                           LocalFavoritesManager().deleteFolder(widget.folder);
                           favPage.folderList?.updateFolders();
-                          context.pop();
                         },
                       );
                     }),
@@ -110,6 +111,18 @@ class _LocalFavoritesPageState extends State<_LocalFavoritesPage> {
                         },
                       );
                     }),
+                MenuEntry(
+                    icon: Icons.upload_file,
+                    text: "Export".tl,
+                    onClick: () {
+                      var json = LocalFavoritesManager().folderToJson(
+                        widget.folder,
+                      );
+                      saveFile(
+                        data: utf8.encode(json),
+                        filename: "${widget.folder}.json",
+                      );
+                    }),
               ],
             ),
           ],

lib/pages/favorites/side_bar.dart

@@ -211,11 +211,13 @@ class _LeftBarState extends State<_LeftBar> implements FolderList {
 
   @override
   void update() {
+    if(!mounted) return;
     setState(() {});
   }
 
   @override
   void updateFolders() {
+    if(!mounted) return;
     setState(() {
       folders = LocalFavoritesManager().folderNames;
       networkFolders = ComicSource.all()