Implement layout.topMargin

This option property lets us set a top margin to a component which can be useful sometimes
when using statusBar.drawBehind.

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

@@ -4,7 +4,7 @@ import android.app.Activity;
 import android.graphics.Color;
 import android.os.Build;
 import android.view.View;
-import android.view.ViewGroup;
+import android.view.ViewGroup.MarginLayoutParams;
 
 import com.reactnativenavigation.parse.Options;
 import com.reactnativenavigation.parse.OrientationOptions;
@@ -40,6 +40,9 @@ public class OptionsPresenter {
         if (options.layout.backgroundColor.hasValue()) {
             view.setBackgroundColor(options.layout.backgroundColor.get());
         }
+        if (options.layout.topMargin.hasValue()) {
+            ((MarginLayoutParams) view.getLayoutParams()).topMargin = options.layout.topMargin.get();
+        }
     }
 
     public void onViewBroughtToFront(View view, Options options) {
@@ -86,7 +89,7 @@ public class OptionsPresenter {
     }
 
     private void setDrawBehindStatusBar(View view, StatusBarOptions statusBar) {
-        ((ViewGroup.MarginLayoutParams) view.getLayoutParams()).topMargin = statusBar.drawBehind.isFalseOrUndefined() ?
+        ((MarginLayoutParams) view.getLayoutParams()).topMargin = statusBar.drawBehind.isFalseOrUndefined() ?
                 UiUtils.getStatusBarHeight(activity) :
                 0;
     }

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

@@ -79,7 +79,7 @@ public class StackOptionsPresenter {
                 topBar.show();
             }
         }
-        if (options.drawBehind.isTrue()) {
+        if (options.drawBehind.isTrue() && !componentOptions.layout.topMargin.hasValue()) {
             component.drawBehindTopBar();
         } else if (options.drawBehind.isFalseOrUndefined()) {
             component.drawBelowTopBar(topBar);