fixed: season fanart can't change...

... if episodes are not in a separate season folder
fixed: YAMJ season fanart in edit window
fixed: deletion of posters and fanarts

- all known posters and fanart filenames are now deleted properly.
- <movie>-fanart.jpg for YAMJ is now saved correctly
Fix for Season / Episode fanart/poster delete

Why we have 3 identical dialogs!!!! :(