Start app (#2927)

* WIP

* Apply default options when screen options are null

* modal animations

* fix tests

* refactor

* refactor

* refactor

* refactor

* test fix

* topBar anim

* child disappear bug

* Update app.js

* Update WelcomeScreen.js

* fix tests

* bottom tabs

* stack id

* fix test

* refactoring

* merge fix

* Update app.js

* merge

* comment to fix test

* merge options

* start app anim

* anim

lib/android/app/src/main/java/com/reactnativenavigation/anim/BaseAnimator.java

 
 class BaseAnimator {
 
-    AnimationsOptions options = new AnimationsOptions();
+    protected AnimationsOptions options = new AnimationsOptions();
 
     private static final int DURATION = 300;
     private static final DecelerateInterpolator DECELERATE_INTERPOLATOR = new DecelerateInterpolator();

lib/android/app/src/main/java/com/reactnativenavigation/anim/NavigationAnimator.java

         super(context);
     }
 
+    public NavigationAnimator(Context context, AnimationsOptions options) {
+        super(context);
+        this.options = options;
+    }
+
     public void animatePush(final View view, @Nullable final AnimationListener animationListener) {
         view.setVisibility(View.INVISIBLE);
         AnimatorSet set;
         set.start();
     }
 
+    public void animateStartApp(View view, @Nullable final AnimationListener animationListener) {
+        view.setVisibility(View.INVISIBLE);
+        AnimatorSet set = options.startApp.getAnimation(view);
+        set.addListener(new AnimatorListenerAdapter() {
+            @Override
+            public void onAnimationStart(Animator animation) {
+                view.setVisibility(View.VISIBLE);
+            }
+
+            @Override
+            public void onAnimationEnd(Animator animation) {
+                if (animationListener != null) animationListener.onAnimationEnd();
+            }
+        });
+        set.start();
+    }
+
     public void setOptions(AnimationsOptions options) {
         this.options = options;
     }

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

 import android.app.Activity;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.view.View;
 import android.view.ViewGroup;
 import android.widget.FrameLayout;
 
 import com.facebook.react.bridge.Promise;
+import com.reactnativenavigation.anim.NavigationAnimator;
+import com.reactnativenavigation.parse.AnimationsOptions;
 import com.reactnativenavigation.parse.Options;
 import com.reactnativenavigation.presentation.NavigationOptionsListener;
 import com.reactnativenavigation.presentation.OverlayManager;
         }
 
         root = viewController;
-        getView().addView(viewController.getView());
-        promise.resolve(viewController.getId());
+        View view = viewController.getView();
+
+        AnimationsOptions animationsOptions = viewController.options.animationsOptions;
+        if (animationsOptions.startApp.hasValue()) {
+            getView().addView(view);
+            new NavigationAnimator(viewController.getActivity(), animationsOptions)
+                    .animateStartApp(view, () -> promise.resolve(viewController.getId()));
+        } else {
+            getView().addView(view);
+            promise.resolve(viewController.getId());
+        }
     }
 
     public void setDefaultOptions(Options defaultOptions) {

playground/android/gradle.properties

 # Disable incremental resource processing as it broke relase build
 # https://github.com/react-community/react-navigation/issues/1976
 # https://developer.android.com/studio/build/gradle-plugin-3-0-0.html
-android.enableAapt2=false

playground/src/app.js

   Navigation.events().onAppLaunched(() => {
     Navigation.setDefaultOptions({
       _animations: {
+        startApp: {
+          y: {
+            from: 1000,
+            to: 0,
+            duration: 500,
+            interpolation: 'accelerate',
+          },
+          alpha: {
+            from: 0,
+            to: 1,
+            duration: 500,
+            interpolation: 'accelerate'
+          }
+        },
         push: {
           topBar: {
             id: 'TEST',