This fixes CommandBar display for some playbacks on windows phone

Which prevents a DisposedObjectException to be thrown and to terminate the program

This fixes a potential deadlock

Fix #129

It's never updated, and should we actually need something like that, we'd better rely on a VLC state instead

Also, don't save it, since we're restoring it...

The command bar aspect is the same with or without it

We need to update PlayingType when we actually know what type of media we're playing
Update relevent properties when the current media changes. Using OnPlaylistChanged event handler for that updates notifies changes for properties that couldn't have changed

This depends on the media library, and could fail easily.