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/foundation/favorites.dart

@@ -4,6 +4,7 @@ import 'package:flutter/foundation.dart';
 import 'package:sqlite3/sqlite3.dart';
 import 'package:venera/foundation/appdata.dart';
 import 'package:venera/foundation/image_provider/local_favorite_image.dart';
+import 'package:venera/foundation/local.dart';
 import 'package:venera/foundation/log.dart';
 import 'dart:io';
 
@@ -496,6 +497,22 @@ class LocalFavoritesManager with ChangeNotifier {
     notifyListeners();
   }
 
+  Future<int> removeInvalid() async {
+    int count = 0;
+    await Future.microtask(() {
+      var all = allComics();
+      for(var c in all) {
+        var comicSource = c.type.comicSource;
+        if ((c.type == ComicType.local && LocalManager().find(c.id, c.type) == null) 
+          || (c.type != ComicType.local && comicSource == null)) {
+          deleteComicWithId(c.folder, c.id, c.type);
+          count++;
+        }
+      }
+    });
+    return count;
+  }
+
   Future<void> clearAll() async {
     _db.dispose();
     File("${App.dataPath}/local_favorite.db").deleteSync();