Feature request: need wait() for Selenium exctension

I've faced a situation when waitForElement() is practically useless, as the element to "intercept" is actually loaded inside an iframe. This is with Google's reCaptcha widget.

```php
// ...
->andClick('recaptcha_box_1')
->andWait(/* let say, 3000 milliseconds */) // missing feature :-(
->andClick('Submit')
// ...
