hide, don't disable scroll for media players page

ScrollViewer.VerticalScrollBarVisibility=Disabled means scrolling isn't
allowed at all. It should be Hidden instead to ensure that users can
still see past the first few entries if they have many external media
players configured (ex. using GameBrowser or MB Bookshelf)
Merge pull request #204 from coldacid/master

hide, don't disable scroll for media players page