Track Ordering Issue with DiscSubtitle

[tiefling]

I've been using a temporary workaround to map DiscSubtitle to another field for now - I thibk the handling issue is Serento side and it's due to get fixed in the next release.

`upnpCustom: multiTag={Artist,Genre}`

@simbun - What's the issue with this - I've had it for a while so excuse my brain, but isn't it supposed to allow Artist and Genre to have multiple values? It's not a Serento recommendation.