title: get notification when permissions change in metro app
body: <p>I'm working at a Win 8 Metro App with c#.</p>
  
  <p>in my App I use the geolocation Service to get the current coordinates of the users position. The first time you start the App you'll be asked for the permissions.
  This all works fine and I get the coordinates without a problem.</p>
  
  <p>Now I want to give the user a message as soon as the permissions changes.
  How to do this?</p>