Not Real - Hooking In Sounds Review

@kadst43 - Not a real commit, just looking for guidance/scolding on placement of sounds and referencing the soundManager. Sounds are playing though! (Weird stuff happening with the diff in scenario.js - dunno what's up with that.)
For this sound, we fire an event called `batteryChanged` that takes the new value as a parameter. You can do something like this in rover.js:
```
this.batteryChanged = function ( value ) {
    If ( value <= 4) {
        soundManager.playSound( 'uiLowBattery' );
    }
}
```
That would be allow you to only have to call it from one spot. I would play as many sounds as possible in this way.