added tab selected event (#605)

* added tab selected event

* changed event name to `bottomTabSelected`

ios/RCCTabBarController.m

     [[[RCCManager sharedInstance].getBridge uiManager] configureNextLayoutAnimation:nil withCallback:^(NSArray* arr){} errorCallback:^(NSArray* arr){}];
   });
   
+  [RCCTabBarController sendScreenTabChangedEvent:viewController];
+  
   return YES;
 }
 
     }
 }
 
++(void)sendScreenTabChangedEvent:(UIViewController*)viewController {
+  if ([viewController.view isKindOfClass:[RCTRootView class]]){
+    RCTRootView *rootView = (RCTRootView *)viewController.view;
+    
+    if (rootView.appProperties && rootView.appProperties[@"navigatorEventID"]) {
+      NSString *navigatorID = rootView.appProperties[@"navigatorID"];
+      NSString *screenInstanceID = rootView.appProperties[@"screenInstanceID"];
+      
+      [[[RCCManager sharedInstance] getBridge].eventDispatcher sendAppEventWithName:rootView.appProperties[@"navigatorEventID"] body:@
+       {
+         @"id": @"bottomTabSelected",
+         @"navigatorID": navigatorID,
+         @"screenInstanceID": screenInstanceID
+       }];
+    }
+  }
+  
+  if ([viewController isKindOfClass:[UINavigationController class]]) {
+    UINavigationController *navigationController = (UINavigationController*)viewController;
+    UIViewController *topViewController = [navigationController topViewController];
+    [RCCTabBarController sendScreenTabChangedEvent:topViewController];
+  }
+}
+
+
 @end