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.
Or if you would prefer to simply hide the battery percentage if it isn't present then...
~~~
delta = (currentBGDelta > 0 ? '+' : '') + currentBGDelta + " mg/dL";
if (currentBattery) delta = delta + " " + currentBattery + "%";
~~~