[FR] add more metrics

```
This might be not-so-important, but would fulfill all the features of the
good-old (yet deprecated) Android Battery Dog.
1. Add Charge% graph to quickly look the charge and discharge periods. (Most
important values for most users).
2. Maybe add some more metrics. This could include
http://code.google.com/p/currentwidget/issues/detail?id=11 and also BattV,
Charge/Discharge rate in %/hour, ...

Thanks a lot for the app, the Android Battery Dog replacement!
```

Original issue reported on code.google.com by `ildar.mulyukov` on 18 Jun 2013 at 5:00