Allow Custom Messages

Allow usage of adding a ``messages`` function to any FormRequest item.

```php
	/**
	 * Get the error messages that apply to the request.
	 * 
	 * @return array
	 */
	public function messages() {
		return [
				'email.required' => 'We need to know your e-mail address!',
		];
	}
```

Request #5592 :)