Don't crop thumbnails in list view for non-movie videos.

I have a lot of downloaded videos with 1920 x 1080 pixel thumbnail files alongside. In list view Infuse chops the middle third out of the thumbnail and uses that. There’s plenty of empty space on the left of the screen, where the cast list goes if it is a movie, which could be used to show the full thumbnail.

(If this was implemented I’d still want to be able to add description metadata, which could appear in the same area it does now.)