cmparts: Make CMParts searchable

 * Implement a SearchIndexablesProvider to allow the Settings app
   to crawl our resources.
 * Add all missing metadata where necessary so resources can be
   indexed.

Change-Id: Ic8f304a7995b269f476eda6306d11b366621f4b0
diff --git a/res/xml/button_settings.xml b/res/xml/button_settings.xml
index c58650e..de9c062 100644
--- a/res/xml/button_settings.xml
+++ b/res/xml/button_settings.xml
@@ -14,7 +14,9 @@
      limitations under the License.
 -->
 
-<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+        android:key="button_settings"
+        android:title="@string/button_pref_title">
 
     <SwitchPreference
         android:key="disable_nav_keys"