Set RelativeLayout as TopBar root component

motivation: ability to add react view as TopBar background

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

 
     private void applyTopBarOptions(TopBarOptions options, AnimationsOptions animationOptions, Component component) {
         if (options.title.text.hasValue()) topBar.setTitle(options.title.text.get());
-        if (options.title.component.hasValue())
-            topBar.setComponent(options.title.component.get(), options.title.alignment);
+        if (options.title.component.hasValue()) topBar.setComponent(options.title.component.get(), options.title.alignment);
         topBar.setBackgroundColor(options.background.color);
         topBar.setTitleTextColor(options.title.color);
         topBar.setTitleFontSize(options.title.fontSize);
     }
 
     private void applyTopTabOptions(TopTabOptions topTabOptions) {
-        if (topTabOptions.fontFamily != null) {
-            topBar.setTopTabFontFamily(topTabOptions.tabIndex, topTabOptions.fontFamily);
-        }
+        if (topTabOptions.fontFamily != null) topBar.setTopTabFontFamily(topTabOptions.tabIndex, topTabOptions.fontFamily);
     }
 
     public void onChildWillDisappear(Options disappearing, Options appearing, @NonNull ChildDisappearListener childDisappearListener) {

lib/android/app/src/main/java/com/reactnativenavigation/views/TopBar.java

 import android.support.v4.view.ViewPager;
 import android.support.v7.widget.Toolbar;
 import android.view.View;
+import android.widget.RelativeLayout;
 import android.widget.TextView;
 
 import com.reactnativenavigation.anim.AnimationListener;
 import com.reactnativenavigation.anim.TopBarCollapseBehavior;
 import com.reactnativenavigation.interfaces.ScrollEventListener;
 import com.reactnativenavigation.parse.AnimationOptions;
-import com.reactnativenavigation.parse.AnimationsOptions;
 import com.reactnativenavigation.parse.TitleOptions;
 import com.reactnativenavigation.parse.params.Button;
 import com.reactnativenavigation.parse.params.Color;
 import com.reactnativenavigation.parse.params.Fraction;
 import com.reactnativenavigation.parse.params.Number;
+import com.reactnativenavigation.utils.CompatUtils;
 import com.reactnativenavigation.viewcontrollers.ReactViewCreator;
 import com.reactnativenavigation.viewcontrollers.TitleBarReactViewController;
 import com.reactnativenavigation.viewcontrollers.TopBarButtonController;
 
 @SuppressLint("ViewConstructor")
 public class TopBar extends AppBarLayout implements ScrollEventListener.ScrollAwareView {
-    private final TitleBar titleBar;
+    private TitleBar titleBar;
     private final TopBarCollapseBehavior collapsingBehavior;
     private TopBarAnimator animator;
     private TopTabs topTabs;
+    private RelativeLayout root;
     private StackLayout parentView;
 
     public TopBar(final Context context, ReactViewCreator buttonCreator, TitleBarReactViewCreator titleBarReactViewCreator, TopBarButtonController.OnClickListener onClickListener, StackLayout parentView) {
         super(context);
         collapsingBehavior = new TopBarCollapseBehavior(this);
-        topTabs = new TopTabs(getContext());
         animator = new TopBarAnimator(this);
         this.parentView = parentView;
-        titleBar = createTitleBar(context, buttonCreator, titleBarReactViewCreator, onClickListener);
-        addView(titleBar);
+        createLayout(buttonCreator, titleBarReactViewCreator, onClickListener);
+    }
+
+    private void createLayout(ReactViewCreator buttonCreator, TitleBarReactViewCreator titleBarReactViewCreator, TopBarButtonController.OnClickListener onClickListener) {
+        topTabs = new TopTabs(getContext());
+        titleBar = createTitleBar(getContext(), buttonCreator, titleBarReactViewCreator, onClickListener);
+        titleBar.setId(CompatUtils.generateViewId());
+        root = new RelativeLayout(getContext());
+        root.addView(titleBar, MATCH_PARENT, WRAP_CONTENT);
+        addView(root, MATCH_PARENT, WRAP_CONTENT);
         setContentDescription("TopBar");
     }
 
     public void initTopTabs(ViewPager viewPager) {
         topTabs = new TopTabs(getContext());
         topTabs.init(viewPager);
-        addView(topTabs);
+        RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(MATCH_PARENT, WRAP_CONTENT);
+        lp.addRule(RelativeLayout.BELOW, titleBar.getId());
+        root.addView(topTabs, lp);
     }
 
     public void enableCollapse(ScrollEventListener scrollEventListener) {