plex_exporter_importer.py: Allow alternate name of exported/importing posters/images

[gitttt54]

Hello,

coming from here, I'd like to request an additional feature for the great poster_exporter_importer script.

Can you add an option to define the artist and album image name? Like --AlbumImageName cover_front.jpg and --ArtistImageName Artist.jpg So users can define their own filenames to be imported (and maybe exported).

Its simply because: I can not rename all the images, because other software scripts won't work then. And I share (better, they share with me) folders with friends, which surely have their own scripts and would not like me to rename all their image files.

Thank you!