Fix problem where persister is not saved or retrieved from config file

Author: Paul Verdu

src/DataDefinitionsBundle/Model/ImportDefinition/Dao.php

@@ -152,6 +152,7 @@ public function save()
                 'forceLoadObject',
                 'loader',
                 'fetcher',
+                'persister',
             ];
 
             foreach ($dataRaw as $key => $value) {

src/DataDefinitionsBundle/Resources/config/serializer/Model.ImportDefinition.yml

@@ -50,3 +50,7 @@ Wvision\Bundle\DataDefinitionsBundle\Model\ImportDefinition:
             expose: true
             type: boolean
             groups: [Detailed]
+        persister:
+            expose: true
+            type: string
+            groups: [Detailed]