FormElement as Filters

[gnomium]

I'd like to be more flexible with filters and use other inputs besides Text and Select elements,
For instance when you want to filter by Date you can use a Datepicker.
I added the option to pass a FormElement to the renderer instead of a String or an Array.

usage would be

    'createdate' =>        array('tableAlias' => 'p', 'title' => 'createdate', 'filters' => new Element\Date('zff_createdate')),