Add an Activity to handle Intents to invoke the Deletion Helper.

This will allow apps to launch the deletion helper when they need to
have space freed up.

To launch the activity using an intent, you can set it as follows:
Intent intent = new Intent(Settings.ACTION_DELETION_HELPER_SETTINGS);
startActivity(intent);

This intent should bring up the Deletion Helper.

Bug: 28675265
Change-Id: I781615ccad4ca1fcae97817ecb823e5dcad67b5b

src/com/android/settings/Settings.java

@@ -139,6 +139,7 @@ public class Settings extends SettingsActivity {
     public static class ScreenLockSuggestionActivity extends ChooseLockGeneric { /* empty */ }
     public static class WallpaperSettingsActivity extends SettingsActivity { /* empty */ }
     public static class ManagedProfileSettingsActivity extends SettingsActivity { /* empty */ }
+    public static class DeletionHelperActivity extends SettingsActivity { /* empty */ }
 
     // Categories.
     public static class WirelessSettings extends SettingsActivity { /* empty */ }