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

pubspec.yaml

@@ -65,6 +65,10 @@ dependencies:
       ref: 285f87f15bccd2d5d5ff443761348c6ee47b98d1
   battery_plus: ^6.2.0
   local_auth: ^2.3.0
+  flutter_saf:
+    git: 
+      url: https://github.com/pkuislm/flutter_saf.git
+      ref: 829a566b738a26ea98e523807f49838e21308543
 
 dev_dependencies:
   flutter_test: