Add anomaly icon for PowerGaugePreference

When the app contains anomaly, we should show anomaly icon(triangle
alert).

This cl also extracts a new method refreshAppListGroup from refreshUi.
New method is used to only refresh appListGroup. Reason for this action:

1. Improve performance(partial refresh)
2. We init AnomalyLoader in refreshUi, invoke refreshUi in
onLoadFinish will create infinite loop.

Bug: 36924669
Test: RunSettingsRoboTests
Change-Id: If54c89349e21763ca714123ac6ae884bd0f6a377

res/layout/preference_widget_summary.xml

@@ -18,6 +18,8 @@
     android:id="@+id/widget_summary"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
+    android:drawablePadding="8dp"
+    android:gravity="center_vertical|end"
     android:textAlignment="viewEnd"
     android:textAppearance="?android:attr/textAppearanceSmall"
     android:textColor="?android:attr/textColorSecondary" />