Enforce Keyguard policy in Notification Settings

- Applied getKeyguardDisabledFeatures for notification settings and
    notification setup page (after settings a screenlock)
- If a notification settings is disabled, the next least secure setting
    will be chosen
- Although KEYGUARD_DISABLE_UNREDACTED_NOTIFICATIONS can be set be
    profile, it will not be reflected in both settings page. This is
    because it does not affect the owner (user 0), as mentioned in
    DevicePolicyManagerService.PROFILE_KEYGUARD_FEATURES_AFFECT_OWNER
- Skip RedactionInterstitial if there is <= 1 options for the user
- Tested with both Setup wizard and settings case, both pattern and
    password, as well as toggling the policy on and off

Bug: 19307118
Bug: 17099898

Change-Id: If640d5576caa0163e9942569f7b4643a30bbfe0a

src/com/android/settings/DropDownPreference.java

@@ -126,6 +126,10 @@ public class DropDownPreference extends Preference {
         mValues.add(value);
     }
 
+    public int getItemCount() {
+        return mAdapter.getCount();
+    }
+
     public void clearItems(){
         mAdapter.clear();
         mValues.clear();