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
