add support to display the volume(widget) states as emoji characters

the advantage is that don't require icons.

![volume up](http://d.fsck.com.ar/3jGyK.png "Volume Up")
![volume med](http://d.fsck.com.ar/r1hIn.png "Volume Med")
![volume mute](http://d.fsck.com.ar/q1D9x.png "Volume Mute")