Add column option, definition in config & adapt form

Exemple for configuration :

```
chill_custom_fields:
    customizables_entities:
        -
            class: Chill\ReportBundle\Entity\Report
            name: ReportEntity
            options:
                summary_fields: {key: abc, form_type: text, form_options: { required: false }}
```

Form/CustomFieldsGroupType.php

@@ -6,6 +6,8 @@ use Symfony\Component\Form\AbstractType;
 use Symfony\Component\Form\FormBuilderInterface;
 use Symfony\Component\OptionsResolver\OptionsResolverInterface;
 use Symfony\Component\Translation\TranslatorInterface;
+use Symfony\Component\Form\FormEvents;
+use Symfony\Component\Form\FormEvent;
 
 
 class CustomFieldsGroupType extends AbstractType
@@ -32,18 +34,50 @@ class CustomFieldsGroupType extends AbstractType
     public function buildForm(FormBuilderInterface $builder, array $options)
     {
         //prepare translation
-        $customizableEntites = array();
+        $entities = array();
+        $customizableEntities = array();
         
         foreach($this->customizableEntities as $key => $definition) {
-            $customizableEntites[$definition['class']] = $this->translator->trans($definition['name']);
+            $entities[$definition['class']] = $this->translator->trans($definition['name']);
+            $customizableEntities[$definition['class']] = $definition;
         }
         
         $builder
             ->add('name', 'translatable_string')
             ->add('entity', 'choice', array(
-                'choices' => $customizableEntites
+                'choices' => $entities
             ))
         ;
+
+        $builder->addEventListener(FormEvents::POST_SET_DATA, function(FormEvent $event) 
+                use ($customizableEntities, $builder){
+                    $form = $event->getForm();
+                    $group = $event->getData();
+                    
+                    if (count($customizableEntities[$group->getEntity()]['options']) > 0) {
+                        $optionBuilder = $builder
+                                ->getFormFactory()
+                                ->createBuilderForProperty(
+                                        'Chill\CustomFieldsBundle\Entity\CustomFieldsGroup', 
+                                        'options'
+                                        )
+                                ->create('options', null, array(
+                                        'compound' => true, 
+                                        'auto_initialize' => false,
+                                        'required' => false)
+                                    );
+                    }
+                    
+                    foreach($customizableEntities[$group->getEntity()]['options'] as $key => $option) {
+                                $optionBuilder
+                                    ->add($key, $option['form_type'], $option['form_options'])
+                            ;
+                    }
+                    if (isset($optionBuilder) && $optionBuilder->count() > 0) {
+                        $form->add($optionBuilder->getForm());
+                    }
+                    
+                });
     }
     
     /**