Bug 1051793 - [CMAS] Plug in real CMAS input to the CMAS application

- Add cellbroadcast system message handler
- Removed unused styling and testing UI
- Add localization properties
nit: Julien always corrected me on this in the past :)
```
 window.navigator.mozSetMessageHandler(
   'cellbroadcast-received',
   onCellbroadcast
 );
```