If navigating away from a musician's timeline on Facebook to get a quick listen isn't your favorite activity, you're in luck. The folks in Palo Alto dropped a "Listen" button on artist pages today, giving you access to popular tracks instantly. Situated right beside the ever important "Like" button, the new feature first asks if you'd like to open your favorite music-streaming app -- either Spotify, MOG or Rdio. If you've yet to link a se
