Revert "Revert "Add 'uk_birthday' validator that accepts DD/MM/YYYY form...

Reverts DoSomething/dosomething#3085, which in turn reverted DoSomething/dosomething#3084. 

[So basically...](http://inception.davepedu.com/noflash.php)

For review: @sergii-tkachenko 
I think it's better to make it compact, [example](https://api.drupal.org/api/drupal/includes%21common.inc/function/drupal_add_js/7):

```php
drupal_add_js(array('myModule' => array('key' => 'value')), 'setting');
```