Please add Webforms Repetition Model

Issue Summary

I would love to be able to use the repetition model for webforms (http://www.whatwg.org/specs/web-forms/current-work/#repeatingFormControls). Unfortunately, this got removed from the HTML5 proposal when they integrated the webforms section, but that doesn't mean we can't build it. There's an implementation already out there (http://code.google.com/p/webforms2/), could it perhaps be a integrated or adapted to this module?

Basically, for the section of the form you want to make repeatable, you create a template. There'd be an Add button that copies the template and inserts it in the form. There'd also be a Delete button for each copy, allowing you to remove it from the form. The specs also describe moving the "rows" up and down, but that to me would be a lower on the priority list.

The reason I'm looking for this is I'd like to build a form where an end user can submit details (name, age, etc) for an arbitrary number of people (family members) on the same form when they request registration related information for our club. I would prefer this information to be structured in appropriate fields, rather than unstructured in a big textarea.