[iOS] Added fade transition animation between screens (#1367)

* [iOS] Added fade transition animation between screens

* Update docs for #1367

docs/screen-api.md

   titleImage: require('../../img/my_image.png'), //navigation bar title image instead of the title text of the pushed screen (optional)
   passProps: {}, // Object that will be passed as props to the pushed screen (optional)
   animated: true, // does the push have transition animation or does it happen immediately (optional)
+  animationType: 'fade', // does the push have fade transition animation, iOS only (optional)
   backButtonTitle: undefined, // override the back button title (optional)
   backButtonHidden: false, // hide the back button altogether (optional)
   navigatorStyle: {}, // override the navigator style for the pushed screen (optional)
 
 ```js
 this.props.navigator.pop({
-  animated: true // does the pop have transition animation or does it happen immediately (optional)
+  animated: true, // does the pop have transition animation or does it happen immediately (optional)
+  animationType: 'fade', // does the pop have fade transition animation, iOS only (optional)
 });
 ```
 
 
 ```js
 this.props.navigator.popToRoot({
-  animated: true // does the pop have transition animation or does it happen immediately (optional)
+  animated: true, // does the popToRoot have transition animation or does it happen immediately (optional)
+  animationType: 'fade', // does the popToRoot have fade transition animation, iOS only (optional)
 });
 ```
 
   screen: 'example.ScreenThree', // unique ID registered with Navigation.registerScreen
   title: undefined, // navigation bar title of the pushed screen (optional)
   passProps: {}, // simple serializable object that will pass as props to the pushed screen (optional)
-  animated: true, // does the push have transition animation or does it happen immediately (optional)
+  animated: true, // does the resetTo have transition animation or does it happen immediately (optional)
+  animationType: 'fade', // does the resetTo have fade transition animation, iOS only (optional)
   navigatorStyle: {}, // override the navigator style for the pushed screen (optional)
   navigatorButtons: {} // override the nav buttons for the pushed screen (optional)
 });

ios/RCCNavigationController.m

       [self setButtons:rightButtons viewController:viewController side:@"right" animated:NO];
     }
     
-    [self pushViewController:viewController animated:animated];
+    NSString *animationType = actionParams[@"animationType"];
+    if ([animationType isEqualToString:@"fade"])
+    {
+      CATransition *transition = [CATransition animation];
+      transition.duration = 0.25;
+      transition.type = kCATransitionFade;
+      
+      [self.view.layer addAnimation:transition forKey:kCATransition];
+      [self pushViewController:viewController animated:NO];
+    }
+    else
+    {
+      [self pushViewController:viewController animated:animated];
+    }
     return;
   }
   
   // pop
   if ([performAction isEqualToString:@"pop"])
   {
-    [self popViewControllerAnimated:animated];
+    NSString *animationType = actionParams[@"animationType"];
+    if ([animationType isEqualToString:@"fade"])
+    {
+      CATransition *transition = [CATransition animation];
+      transition.duration = 0.25;
+      transition.type = kCATransitionFade;
+      
+      [self.view.layer addAnimation:transition forKey:kCATransition];
+      [self popViewControllerAnimated:NO];
+    }
+    else
+    {
+      [self popViewControllerAnimated:animated];
+    }
     return;
   }
   
   // popToRoot
   if ([performAction isEqualToString:@"popToRoot"])
   {
-    [self popToRootViewControllerAnimated:animated];
+    NSString *animationType = actionParams[@"animationType"];
+    if ([animationType isEqualToString:@"fade"])
+    {
+      CATransition *transition = [CATransition animation];
+      transition.duration = 0.25;
+      transition.type = kCATransitionFade;
+      
+      [self.view.layer addAnimation:transition forKey:kCATransition];
+      [self popToRootViewControllerAnimated:NO];
+    }
+    else
+    {
+      [self popToRootViewControllerAnimated:animated];
+    }
     return;
   }
   
     
     BOOL animated = actionParams[@"animated"] ? [actionParams[@"animated"] boolValue] : YES;
     
-    [self setViewControllers:@[viewController] animated:animated];
+    NSString *animationType = actionParams[@"animationType"];
+    if ([animationType isEqualToString:@"fade"])
+    {
+      CATransition *transition = [CATransition animation];
+      transition.duration = 0.25;
+      transition.type = kCATransitionFade;
+      
+      [self.view.layer addAnimation:transition forKey:kCATransition];
+      [self setViewControllers:@[viewController] animated:NO];
+    }
+    else
+    {
+      [self setViewControllers:@[viewController] animated:animated];
+    }
     return;
   }
   

src/deprecated/platformSpecificDeprecated.ios.js

     titleImage: params.titleImage,
     component: params.screen,
     animated: params.animated,
+    animationType: params.animationType,
     passProps: passProps,
     style: navigatorStyle,
     backButtonTitle: params.backButtonTitle,
 
 function navigatorPop(navigator, params) {
   Controllers.NavigationControllerIOS(navigator.navigatorID).pop({
-    animated: params.animated
+    animated: params.animated,
+    animationType: params.animationType
   });
 }
 
 function navigatorPopToRoot(navigator, params) {
   Controllers.NavigationControllerIOS(navigator.navigatorID).popToRoot({
-    animated: params.animated
+    animated: params.animated,
+    animationType: params.animationType
   });
 }
 
     titleImage: params.titleImage,
     component: params.screen,
     animated: params.animated,
+    animationType: params.animationType,
     passProps: passProps,
     style: navigatorStyle,
     leftButtons: navigatorButtons.leftButtons,