Improve App notification loading

1) Use UiBlocker, for better animations for apps with a lot of channels
2) Only load data in onResume, because the data loading step in some
of the controllers is expensive

Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.notification"
Test: load small channel and large (6000ish) channel app pages
Test: load individual channel pages
Test: load in-app channel shelf UI
Fixes: 215072888
Change-Id: I9a1c96f75b02f94b3ffc529d17d9c0cad7752de1

src/com/android/settings/notification/app/AppChannelsBypassingDndPreferenceController.java

@@ -64,7 +64,7 @@ public class AppChannelsBypassingDndPreferenceController extends NotificationPre
     public AppChannelsBypassingDndPreferenceController(
             Context context,
             NotificationBackend backend) {
-        super(context, backend);
+        super(context, backend, KEY);
     }
 
     @Override
@@ -110,8 +110,8 @@ public class AppChannelsBypassingDndPreferenceController extends NotificationPre
     }
 
     @Override
-    public boolean isAvailable() {
-        return mAppRow != null;
+    public int getAvailabilityStatus() {
+        return mAppRow != null ? AVAILABLE : CONDITIONALLY_UNAVAILABLE;
     }
 
     @Override