Collapse content on fling (#554)

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

 
                     @Override
                     public void onFling(CollapseAmount amount) {
+                        if (screenParams.styleParams.drawScreenBelowTopBar) {
+                            ((CollapsingView) contentView).collapse(amount);
+                        }
                         topBar.collapse(amount);
                     }
                 },

android/app/src/main/java/com/reactnativenavigation/views/CollapsingContentView.java

 import com.reactnativenavigation.params.NavigationParams;
 import com.reactnativenavigation.views.collapsingToolbar.CollapseAmount;
 import com.reactnativenavigation.views.collapsingToolbar.CollapsingView;
+import com.reactnativenavigation.views.collapsingToolbar.CollapsingViewMeasurer;
 import com.reactnativenavigation.views.collapsingToolbar.OnScrollViewAddedListener;
 import com.reactnativenavigation.views.collapsingToolbar.ScrollListener;
 import com.reactnativenavigation.views.collapsingToolbar.ScrollViewDelegate;
 
     @Override
     public float getFinalCollapseValue() {
-        return 0;
+        return ((CollapsingViewMeasurer) viewMeasurer).getFinalCollapseValue();
     }
 
     @Override
     public float getCurrentCollapseValue() {
-        return 0;
+        return getTranslationY();
     }
 
     @Override