Exclude downloaded chapters filter

[Palloxin]

Describe your suggested feature

Downloaded filter doesnt have the exclude (–) feature.

Why

I might want to know what i didnt download.

Other details

An instance where i needed it...
There was an entry with 3k chaps. It had duplicated chapter here and there for a total amount of 23. Watching the downloaded chapter number i found out i didnt download 28 chapters so i wanted to filter all chapter that were not downloaded to create a clean EPUB. I found out that the app doesnt allow it yet so..

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• I have written a short but informative title.
• If this is an issue with a source, I should be opening an issue in the sources repository.
• I have updated the app to version 1.1.18.
• I will fill out all of the requested information in this form.