Add settings VR listener service.

Bug: 22855417
Bug: 26724891

- Adds a settings panel allowing users to toggle the
  enabled/disabled state of each VrListenerService
  component installed.
- If disabled, a VrListenerService will not be bound
  from the framework, even when requested by a VR
  application.

Change-Id: I606eb712c011d160b9fbdd3c0e8fd744c653ef07

src/com/android/settings/Settings.java

@@ -95,6 +95,7 @@ public class Settings extends SettingsActivity {
     public static class NotificationStationActivity extends SettingsActivity { /* empty */ }
     public static class UserSettingsActivity extends SettingsActivity { /* empty */ }
     public static class NotificationAccessSettingsActivity extends SettingsActivity { /* empty */ }
+    public static class VrListenerSettingsActivity extends SettingsActivity { /* empty */ }
     public static class ZenAccessSettingsActivity extends SettingsActivity { /* empty */ }
     public static class ConditionProviderSettingsActivity extends SettingsActivity { /* empty */ }
     public static class UsbSettingsActivity extends SettingsActivity { /* empty */ }