Keep button order

When saving buttons by screen, buttons were stored in a HashMap which doesn't maintain
order.
Closes #3916

lib/android/app/src/main/java/com/reactnativenavigation/presentation/StackOptionsPresenter.java

@@ -34,6 +34,7 @@ import com.reactnativenavigation.views.topbar.TopBar;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -242,7 +243,7 @@ public class StackOptionsPresenter {
 
     private List<TitleBarButtonController> getOrCreateButtonControllers(@Nullable Map<String, TitleBarButtonController> currentButtons, @Nullable List<Button> buttons) {
         if (buttons == null) return null;
-        Map<String, TitleBarButtonController> result = new HashMap<>();
+        Map<String, TitleBarButtonController> result = new LinkedHashMap<>();
         for (Button b : buttons) {
             result.put(b.instanceId, currentButtons != null && currentButtons.containsKey(b.instanceId) ? currentButtons.get(b.instanceId) : createButtonController(b));
         }

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/TitleBarButtonController.java

@@ -8,6 +8,7 @@ import android.support.annotation.NonNull;
 import android.support.annotation.RestrictTo;
 import android.support.v7.widget.ActionMenuView;
 import android.support.v7.widget.Toolbar;
+import android.view.Menu;
 import android.view.MenuItem;
 import android.widget.ImageButton;
 import android.widget.TextView;
@@ -115,7 +116,7 @@ public class TitleBarButtonController extends ViewController<TitleBarReactButton
     }
 
     public void addToMenu(Toolbar toolbar, int position) {
-        MenuItem menuItem = toolbar.getMenu().add(0, position, position, button.text.get(""));
+        MenuItem menuItem = toolbar.getMenu().add(Menu.NONE, position, position, button.text.get(""));
         if (button.showAsAction.hasValue()) menuItem.setShowAsAction(button.showAsAction.get());
         menuItem.setEnabled(button.enabled.isTrueOrUndefined());
         menuItem.setOnMenuItemClickListener(this);