Add possibility to hide empty value in customfield group view rendering

A new parameter is defined :

```
chill_custom_fields:
    show_empty_values_in_views = true|false
```

A new method is added to CustomFieldInterface: `isEmptyValue`. To ease
the dev of new classes, an AbstractCustomField class is created, which
implements the most commons function (currently, only isEmptyValue).

A new Twig Filter is added: `chill_custom_field_is_empty`

The twig filter `chill_custom_fields_group_widget` has a new possibility
in array option : `show_empty`. Default to
chill_custom_fields.show_empty_values_in_view. May be forced by
true/false.

Templating/Twig/CustomFieldRenderingTwig.php

@@ -76,10 +76,21 @@ class CustomFieldRenderingTwig extends \Twig_Extension implements ContainerAware
                 'is_safe' => array(
                     'html'
                 )
+            )),
+            new \Twig_SimpleFunction('chill_custom_field_is_empty', array(
+                $this,
+                'isEmptyValue'
             ))
         ];
     }
     
+    
+    public function isEmptyValue($customFieldorClass, $fields, $slug = null)
+    {
+        return $this->container->get('chill.custom_field.helper')
+            ->isEmptyValue($fields, $customFieldorClass);
+    }
+    
     /* (non-PHPdoc)
      * @see Twig_ExtensionInterface::getName()
      */

Templating/Twig/CustomFieldsGroupRenderingTwig.php

@@ -37,15 +37,25 @@ use Chill\CustomFieldsBundle\Entity\CustomField;
  */
 class CustomFieldsGroupRenderingTwig extends \Twig_Extension implements ContainerAwareInterface
 {
-
+    
     /** @var Container $container The container */
     private $container;
     
     /** @var array $defaultParams The default parameters */
     private $defaultParams = array(
-        'layout' => 'ChillCustomFieldsBundle:CustomFieldsGroup:render.html.twig'
+        'layout' => 'ChillCustomFieldsBundle:CustomFieldsGroup:render.html.twig',
+        'show_empty' => True
     );
     
+    /**
+     * 
+     * @param boolean $showEmptyValues whether the empty values must be rendered
+     */
+    public function __construct($showEmptyValues)
+    {
+        $this->defaultParams['show_empty'] = $showEmptyValues;
+    }
+    
     /*
      * (non-PHPdoc)
      * @see \Symfony\Component\DependencyInjection\ContainerAwareInterface::setContainer()
@@ -92,6 +102,7 @@ class CustomFieldsGroupRenderingTwig extends \Twig_Extension implements Containe
      * @param array $params The parameters for rendering : 
      *  - layout : allow to choose a different layout by default :
      *             ChillCustomFieldsBundle:CustomFieldsGroup:render.html.twig
+     *  - show_empty : force show empty field
      * @return string HTML representation of the custom field group value, as described in 
      * the CustomFieldInterface. Is HTML safe
      */
@@ -102,6 +113,7 @@ class CustomFieldsGroupRenderingTwig extends \Twig_Extension implements Containe
         return $this->container->get('templating')
             ->render($resolvedParams['layout'], array(
             	'cFGroup' => $customFielsGroup,
-            	'cFData' => $fields));
+            	'cFData' => $fields,
+                'show_empty' => $resolvedParams['show_empty']));
     }
 }