更改安卓端的文件访问方式，优化导入逻辑 (#64)

* Refactor import function & Allow import local comics without copying them to local path.

* android: use file_picker instead, support directory access for android 10

* Improve import logic

* Fix sql query.

* Add ability to remove invalid favorite items.

* Perform sort before choosing cover

* Revert changes of "use file_picker instead".

* Try catch on "check update"

* Added module 'flutter_saf'

* gitignore

* remove unsupported arch in build.gradle

* Use flutter_saf to handle android's directory and files, improve import logic.

* revert changes of 'requestLegacyExternalStorage'

* fix cbz import

* openDirectoryPlatform

* Remove double check on source folder

* use openFilePlatform

* remove unused import

* improve local comic's path handling

* bump version

* fix pubspec format

* return null when comic folder is empty

lib/pages/settings/local_favorites.dart

@@ -38,6 +38,16 @@ class _LocalFavoritesSettingsState extends State<LocalFavoritesSettings> {
             for (var e in LocalFavoritesManager().folderNames) e: e
           },
         ).toSliver(),
+        _CallbackSetting(
+          title: "Delete all unavailable local favorite items".tl,
+          callback: () async {
+            var controller = showLoadingDialog(context);
+            var count = await LocalFavoritesManager().removeInvalid();
+            controller.close();
+            context.showMessage(message: "Deleted @a favorite items".tlParams({'a': count}));
+          },
+          actionTitle: 'Delete'.tl,
+        ).toSliver(),
       ],
     );
   }