Sanitize the usage of the screen update timer.

- Make timer static so we only have one.
- Handle starting or stopping of it in the same place where we control if we show player UI or not.
Merge branch 'next' of github.com:kypeli/Podcatcher into next

Conflicts:
	wp7/Podcatcher/CustomControls/PodcastPlayerControl.xaml.cs
Merge branch 'next' of github.com:kypeli/Podcatcher into next
Uups, fix swapped images in player.
Merge branch 'next' of github.com:kypeli/Podcatcher into next
Merge branch 'next' of github.com:kypeli/Podcatcher into next
Merge branch 'next' of github.com:kypeli/Podcatcher into next
Handle download and playback error for HTTP code 301 in WP8.