Allow users to choose the default track name policy. By default, we'll switch
to a new, timestamp-based name. If they change the pref, they'll get the
old-style 'track n' style.
1) Make sure no one but service changes recordingTrackId (which is owned by it)
2) Cache sharedPreferences
3) Clear recordingTrackId if it doesn't correspond to a valid track or the service is not recording
4) More unit tests
Rodrigo Damazio