I would like to add this background by default as a constant in this library or add as a new parameter in build time

```js
var background = Configurator.getSection('background');
SettingsListener.observe('wallpaper.image', background.url,
```

https://github.com/mozilla-b2g/gaia/blob/master/build/applications-data.js#L276
```js
background : {
   url: 'resources/images/backgrounds/default.png'
}