Fix system & back button color (#4592)

* Add color to tintColor

lib/ios/RNNNavigationButtons.m

@@ -44,6 +44,10 @@
 		if(barButtonItem) {
 			[barButtonItems addObject:barButtonItem];
 		}
+		UIColor* color = [self color:[RCTConvert UIColor:button[@"color"]] defaultColor:[defaultStyle.color getWithDefaultValue:nil]];
+		if (color) {
+			self.viewController.navigationController.navigationBar.tintColor = color;
+		}
 	}
 	
 	if ([side isEqualToString:@"left"]) {
@@ -118,6 +122,7 @@
 	if (color) {
 		[textAttributes setObject:color forKey:NSForegroundColorAttributeName];
 		[barButtonItem setImage:[[iconImage withTintColor:color] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal]];
+		barButtonItem.tintColor = color;
 	}
 	
 	NSNumber* fontSize = [self fontSize:dictionary[@"fontSize"] defaultFontSize:[defaultStyle.fontSize getWithDefaultValue:nil]];