Store multiple cover options and undo cover change

[RandomWare]

I have enabled the option to store covers with the audio files. However, only storing one file named 'cover' means that selecting the wrong cover by accident overwrites the already existing cover file, if applicable, without any easy option to undo the mistake. Additionally, some books have covers embedded in their metadata (like some m4b files), but I don't see an easy way to select that cover as an option from the cover settings page.

I propose the following:

1. Store multiple files with different filenames for the cover for the same book.
2. Do not overwrite cover files already in the folder.
3. Have basic file management options to manually delete the wrong cover from the cover settings page.
4. Display any cover that is embedded with the audio file as an option in the cover settings page.