Create a subscribe form for multiple lists.

I would like to let my subscribers select what lists to subscribe to.

It might be:
- Electronic
- Decoration
- Child clothes
- Games etc...
All these options could be a separate contact property of true/false.

But to be able to select one or many you must be able to add checkboxes to the form builder
The current radiobutton doesn't allow you to select more than one, because that's how radiobuttons work...