[mythtv] MythGame rescan drops favorites

[Greg Estabrooks]

> If you set some favorites in MythGame, or if you adjust the genre
> entries in the database, those changes are lost if you scan for new
> games.

 Yup, this is because the gamemetadata table(including favourite status) 
gets wiped during the scan. It's not really a bug but was designed that way.
I might consider a seperate status table at somepoint.