[Audiobookshelf] Playlist/Collection Cover Photo

### Type of Enhancement Web Interface/Frontend ### Describe the Feature/Enhancement Much like a music/audio playlist I think that you should be able to set cover art for the collection, playlist and ideally a series. But I'll settle for just one of the categories. Permitting widescreen artwork and not just square for series and collections I think would be an awesome way to let libraries customize their collections. ### Why would this be helpful? I want to run an official looking ABS server, I want people to come in and see the great art that I've found from fans/official outlets etc. One way to do that is to display it as art for the Book, Series, Collections and Playlists. I think others would enjoy this as well and would foster a community of sharing artwork and stoking people's interests in certain series. ### Future Implementation (Screenshot) Currently I think you don't have to change a lot, just store the image file in the series folder. I don't think you have to alter