Work around stupid NAudio bugs, add progress bar

* Fixed Reflection lag from PlaybackFinished being registered too many
times at PlaybackManager
* Workaround for: https://naudio.codeplex.com/workitem/16455
* Workaround for: https://naudio.codeplex.com/workitem/16456
* Fixed song info not displayed on clicking next when stopped
* Added playback progress display using a DispatcherTimer and a Grid
* Improved FlacFileReader disposing
* Added workarounds for FlacBox for the workarounds for NAudio.
Workaroundception :-(
* Added hack to FlacFileReader to support progress display (still no
seeking)