Add battery stats perference in battery settings page.

Add a preferenceGroup at the bottom of the page, which contains
Screen and Cell usage data.

Bug: 35305983
Test: RunSettingsRoboTests & Screenshot
Change-Id: Ida6e92ddbd7155ec974a2f04c6d6d02ab9dab210

src/com/android/settings/fuelgauge/PowerGaugePreference.java

@@ -59,7 +59,7 @@ public class PowerGaugePreference extends TintablePreference {
     }
 
     public void setPercent(double percentOfTotal) {
-        mProgress = Utils.formatPercentage((int) (percentOfTotal + 0.5));
+        mProgress = Utils.formatPercentage(percentOfTotal, true);
         notifyChanged();
     }