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
Podcast subscriptions export via email in OPML format.
Add support for exporting subscriptions in OPML format to SkyDrive.
Add a setting to choose between exporting via email or to SkyDrive.
End the Head element properly in OPML.
Will use metric date format.
Updated changes file.
Check for NULL in podcast logo when subscribing to a podcast.
Fix typo
Also parse Talk Radio 702's malformed timestamp.
Fix: Default to playable content if MIME type is missing.
Handle icon colors for both light and dark backgrounds.
Uups, fix swapped images in player.
Uups, fix swapped images in player.
Handle feeds that has empty episodes.

Or no pubDate.
Handle podcast feed logos better.
Merge branch 'next' of github.com:kypeli/Podcatcher into next
Handle icon colors for the download queue cancel button too.