Various fab fixes

* Don't show fab of a screen that's pushed to a none active tab
* Change fab when navigating back in the stack with back button
* Add screens before SnackbarAndFabContainer

android/app/src/main/java/com/reactnativenavigation/layouts/BottomTabsLayout.java

         if (getCurrentScreenStack().canPop()) {
             getCurrentScreenStack().pop(true);
             setBottomTabsStyleFromCurrentScreen();
+            EventBus.instance.post(new ScreenChangedEvent(getCurrentScreenStack().peek().getScreenParams()));
             return true;
         } else {
             return false;
         screenStack.push(params, createScreenLayoutParams(params));
         if (isCurrentStack(screenStack)) {
             bottomTabs.setStyleFromScreen(params.styleParams);
+            EventBus.instance.post(new ScreenChangedEvent(params));
         }
-        EventBus.instance.post(new ScreenChangedEvent(params));
     }
 
     @Override
                 @Override
                 public void onScreenPopAnimationEnd() {
                     setBottomTabsStyleFromCurrentScreen();
+                    EventBus.instance.post(new ScreenChangedEvent(getCurrentScreenStack().peek().getScreenParams()));
                 }
             });
             return true;

android/app/src/main/java/com/reactnativenavigation/screens/ScreenStack.java

 import android.util.Log;
 import android.view.View;
 import android.widget.RelativeLayout;
+import android.widget.RelativeLayout.LayoutParams;
 
 import com.reactnativenavigation.NavigationApplication;
 import com.reactnativenavigation.params.ScreenParams;
         keyboardVisibilityDetector = new KeyboardVisibilityDetector(parent);
     }
 
-    public void pushInitialScreenWithAnimation(final ScreenParams initialScreenParams, RelativeLayout.LayoutParams params) {
+    public void pushInitialScreenWithAnimation(final ScreenParams initialScreenParams, LayoutParams params) {
         isStackVisible = true;
         pushInitialScreen(initialScreenParams, params);
         final Screen screen = stack.peek();
         });
     }
 
-    public void pushInitialScreen(ScreenParams initialScreenParams, RelativeLayout.LayoutParams params) {
+    public void pushInitialScreen(ScreenParams initialScreenParams, LayoutParams params) {
         Screen initialScreen = ScreenFactory.create(activity, initialScreenParams, leftButtonOnClickListener);
         initialScreen.setVisibility(View.INVISIBLE);
         addScreen(initialScreen, params);
     }
 
-    public void push(final ScreenParams params, RelativeLayout.LayoutParams layoutParams) {
+    public void push(final ScreenParams params, LayoutParams layoutParams) {
         Screen nextScreen = ScreenFactory.create(activity, params, leftButtonOnClickListener);
         final Screen previousScreen = stack.peek();
         if (isStackVisible) {
-            pushScreenToVisibleStack(params, layoutParams, nextScreen, previousScreen);
+            pushScreenToVisibleStack(layoutParams, nextScreen, previousScreen);
         } else {
             pushScreenToInvisibleStack(layoutParams, nextScreen, previousScreen);
         }
     }
 
-    private void pushScreenToVisibleStack(final ScreenParams params, RelativeLayout.LayoutParams layoutParams,
-                                          final Screen nextScreen, final Screen previousScreen) {
+    private void pushScreenToVisibleStack(LayoutParams layoutParams, final Screen nextScreen, final Screen previousScreen) {
         nextScreen.setVisibility(View.INVISIBLE);
         addScreen(nextScreen, layoutParams);
         nextScreen.setOnDisplayListener(new Screen.OnDisplayListener() {
             @Override
             public void onDisplay() {
-                nextScreen.show(params.animateScreenTransitions, new Runnable() {
+                nextScreen.show(nextScreen.screenParams.animateScreenTransitions, new Runnable() {
                     @Override
                     public void run() {
                         removePreviousWithoutUnmount(previousScreen);
         });
     }
 
-    private void pushScreenToInvisibleStack(RelativeLayout.LayoutParams layoutParams, Screen nextScreen,
-                                            Screen previousScreen) {
+    private void pushScreenToInvisibleStack(LayoutParams layoutParams, Screen nextScreen, Screen previousScreen) {
         nextScreen.setVisibility(View.INVISIBLE);
         addScreen(nextScreen, layoutParams);
         removePreviousWithoutUnmount(previousScreen);
     }
 
-    private void addScreen(Screen screen, RelativeLayout.LayoutParams layoutParams) {
-        parent.addView(screen, layoutParams);
+    private void addScreen(Screen screen, LayoutParams layoutParams) {
+        addScreenBeforeSnackbarAndFabLayout(screen, layoutParams);
         stack.push(screen);
     }
 
+    private void addScreenBeforeSnackbarAndFabLayout(Screen screen, LayoutParams layoutParams) {
+        parent.addView(screen, parent.getChildCount() - 1, layoutParams);
+    }
+
     private void removePreviousWithoutUnmount(Screen previous) {
         previous.preventUnmountOnDetachedFromWindow();
         parent.removeView(previous);