Added support for recently played station tracks

Again, I had serious problems on running useful tests. I would simply add a call like this.
```
            self.mc.get_station_tracks(station_id, num_tracks=1, [TEST_AA_SONG_ID])
```
Would it be OK?
change this to `recently_played=None` and then set it inside the method to avoid the [mutable default arguments](http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments) gotcha