`ValidationError` inherits from `NSObject`

`ValidationError` is now an `NSObject` subclass so that `ValidationDelegate` can declare an argument of type `UITextField:ValidationError`. When `ValidationError` is a Swift only class we get a compile error (in Xcode Version 7.0 GM (7A218)):

> Validator.swift:14:10: Method cannot be a member of an @objc protocol because the type of the parameter cannot be represented in Objective-C

Conflicts:
	Validator/ValidationError.swift

Validator/ValidationError.swift

@@ -9,7 +9,7 @@
 import Foundation
 import UIKit
 
-public class ValidationError {
+public class ValidationError: NSObject {
     public let textField:UITextField
     public var errorLabel:UILabel?
     public let errorMessage:String