Scan for Movie Set Artwork

Movie Set Artwork Scan, simplified and tidied code.

Checks for a [Set Name]-poster.jpg|png and a [Set Name]-fanart.jpg|png inside
the folder where a movie resides (so will pick up set art in a flat structure) also
if the movie resides in a common folder where the folder is named similar to the
set name, it will check for a poster.jpg|png and a fanart.jpg.png.