Default options form that provides the label widget that all fields should have.
Overrides HandlerBase::buildOptionsForm
public function buildOptionsForm(&$form, &$form_state) {
parent::buildOptionsForm($form, $form_state);
unset($form['admin_label']['#fieldset']);
$form['admin_label']['#weight'] = -1;
$form['required'] = array(
'#type' => 'checkbox',
'#title' => t('Require this relationship'),
'#description' => t('Enable to hide items that do not contain this relationship'),
'#default_value' => !empty($this->options['required']),
);
}