Update pebble-js-app.js - Battery Status

Added code to the Pebble app that will allow you to view the current Android battery level of the CGM Uploader.  And display it on the Watchface App.
![batteryindicator](https://cloud.githubusercontent.com/assets/8139553/3647756/4005b20a-1102-11e4-8865-f8e276af92f7.png)