Add Search / Indexing to Data Usage / Mobile Hotspots

- implement a BaseSearchIndexProvider and pass all the needed
strings to index (including the Wi-Fi SSIDs)

Change-Id: Ic7a640c76cd7c2af77585e87e216b283af61a29e

src/com/android/settings/Utils.java

@@ -66,7 +66,7 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Locale;
 
-public class Utils {
+public final class Utils {
 
     /**
      * Set the preference's title to the matching activity's label.