mod to provide On Deck TV episode

mod to provide On Deck TV episode rather than the first unwatched
episode.
Pros: matches On Deck feature from Plex, makes sloppy/disorderly
libraries less of a penalty for users.
Cons: adds about 60% processing time to the fetch_tvshows_recommended
method (about 0.12 seconds on my i5 laptop and about 5 seconds on my
Raspberry Pi).