message: Ensured replacee appears above replaced
  The replace and remove/add animation runs in wrong order - the replaced scene appears on top of the replacee. Added an elevation to scenes so that later scenes always appear on top of earlier
diff: @@ -13,6 +13,7 @@ import android.util.Pair;
  import android.view.View;
  import android.view.ViewGroup;
  +import androidx.core.view.ViewCompat;
  import androidx.fragment.app.Fragment;
  import androidx.fragment.app.FragmentActivity;
  import androidx.fragment.app.FragmentManager;
  @@ -68,6 +69,7 @@ public class NavigationStackView extends ViewGroup {
  @Override
  public void addView(View child, int index) {
  SceneView scene = (SceneView) child;
  + ViewCompat.setElevation(scene, index);
  sceneKeys.add(index, scene.sceneKey);
  scenes.put(scene.sceneKey, scene);
  }
  @@ -138,7 +140,8 @@ public class NavigationStackView extends ViewGroup {
  FragmentManager fragmentManager = ((FragmentActivity) mainActivity).getSupportFragmentManager();
  FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
  fragmentTransaction.setCustomAnimations(enter, exit, popEnter, popExit);
  - fragmentTransaction.replace(((ViewGroup) this.getParent()).getId(), new SceneFragment(scene), key);
  + fragmentTransaction.remove(fragmentManager.findFragmentByTag(oldKey));
  + fragmentTransaction.add(((ViewGroup) this.getParent()).getId(), new SceneFragment(scene), key);
  fragmentTransaction.addToBackStack(String.valueOf(crumb));
  fragmentTransaction.commit();
  }
  