service: Avoid null intent onStartCommand().

Null intent will be sent to services in the case of some crashes.
StringUtils: Clean up warnings.
MPD.java: Fix Add & Play.

This fixes a small bug added (abd63e8) where Add & Play broke.
NowPlaying*Fragment: If stopped and the playlist changes, initiate a update.

If stopped, and the playlist changes, initiate a track & cover information
update.
dmix: Travis update.

Now that I've RTFM for Travis CI, there was an easier/better way, though,
the disadvantage is it will no longer autodetect the build tools version.
MPDroidService: Before stopSelf(), stopForeground() needs to run.