Show shadow when entity header starts scrolling.

- Add a controller to manage add/remove onScrollChangedListener to
  recyclerviews.
- When recyclerview on each screen is scrolled to top, set actionbar
  elevation to 0, otherwise set it to non-zero.
- When screen is moved to background, detach the listener.
- Use the controller in entity header.

Change-Id: Iecf194d885098c98c392810f62893ae9189f3936
Fix: 37670670
Test: make RunSettingsRoboTests

src/com/android/settings/accounts/AccountDetailDashboardFragment.java

@@ -109,7 +109,7 @@ public class AccountDetailDashboardFragment extends DashboardFragment {
         mRemoveAccountController = new RemoveAccountPreferenceController(context, this);
         controllers.add(mRemoveAccountController);
         controllers.add(new AccountHeaderPreferenceController(
-                context, getActivity(), this, getArguments()));
+                context, getLifecycle(), getActivity(), this, getArguments()));
         return controllers;
     }