Add remove_art_file configuration property to EmbedArt plugin

[jackwilsdon]

Adds a configuration property for automatically removing album art files after embedding them.

embedart:
  remove_art_file: yes|no

[sampsyo]

This looks great; thank you for the contribution!

Can you please also add a note to the documentation describing the option (and why someone might want to use it)?

[jackwilsdon]

I've improved the description of remove_art_file with a small section on it's purpose (to be used alongside fetchart).

[jackwilsdon]

There seems to be an issue with the fact that album.artpath isn't set back to None, so other plugins (e.g. convert) get confused when the art doesn't exist.

[jackwilsdon]

So I have tried setting album.artpath to None, however it isn't saved. Is there a method I need to call to save the data? Looks like calling album.store() does the trick.

[sampsyo]

So it does! Awesome work; thank you for fixing that last detail. ✨