implement prefix for formtypes

[craigh]

\Zikula\Bundle\DynamicFormPropertyBundle\Entity\AbstractDynamicPropertySpecification has a stub for prefix and these are used in \Zikula\Bundle\DynamicFormPropertyBundle\Form\Type\InlineFormDefinitionType when creating the form type name.

            $builder->add($prefix.$fieldSpecification->getName(), $fieldSpecification->getFormType(), $fieldOptions);

but there is no current way to set the value.