New features:
1. Support new iOS 14 widgets: show your favorite book or recent books on home screen
2. Filter books by EPUB generated or not
3. Audio can be hidden
4. Add link to audio in paragraph
5. Default chapter in group can be deleted
6. Default chapter in group will not be generated automatically
7. Default chapter in group will not be default chapter anymore after importing or duplicating book
8. Auto-generated group index page can be disabled (Book Style > Group Index Page)
9. Bug fix
