Adding the ability to pass a class to the DtDdWrapper for it to use on the DT or the DD.

It's always nice to be able to reference a given element or type of element, be it for CSS styling or JS handling.

For example,DtDDWrapper is used by default for submit buttons, and one could often want not to display at all the (empty) DT, or center the submit button within its wrapping DD.

It could be used like so :

$submit->getDecorator('DtDdWrapper')->setOption('dtClass','submit-dt-wrapper');
$submit->getDecorator('DtDdWrapper')->setOption('ddClass','submit-dd-wrapper');