implement options_definition on date_ical_plugin_style_ical_feed so views export works.

I was trying to figure out why my exported ical view display was missing its options when moving between environments -- we use features extensively for this -- and it turns out the date_ical_plugin_style_ical_feed does not implement "option_definition" which is required for exports.

I would think something like the following would work :

function option_definition() {
  $options = parent::option_definition();
  $options['cal_name'] = array('default' => array());
  $options['no_calname'] = array('default' => array());
  $options['disable_webcal'] = array('default' => array());
  return $options;
}