Clear default value on focus in form generator

This simple extension adds a "Clear default value" option to the form generator fields "Textfield" and "Textarea". If you check the box, the default value will be hidden when the users clicks inside the field.

Depending on the browser, the styling must be done differently! On newer browser you can target the placeholder (::-webkit-input-placeholder or :-moz-placeholder), old browsers will keep the CSS class "cleardefault".