Allow below divider for all EntityHeader

- Create an method in LayoutPreference let other class can
  set divider status.
- EntityHeaderController will allow to have a below divider
  by default.

Test: visual, robotest
Bug: 116346008
Change-Id: Ic041b8fef8d22ce1b7ea48eedfbe97c708c41ce7

src/com/android/settings/widget/EntityHeaderController.java

@@ -238,6 +238,7 @@ public class EntityHeaderController {
         pref.setOrder(-1000);
         pref.setSelectable(false);
         pref.setKey(PREF_KEY_APP_HEADER);
+        pref.setAllowDividerBelow(true);
         return pref;
     }