fix #1502 avoid duplicate entry and store pocket url in config

src/Wallabag/ImportBundle/DependencyInjection/Configuration.php

@@ -2,6 +2,7 @@
 
 namespace Wallabag\ImportBundle\DependencyInjection;
 
+use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 
@@ -12,6 +13,22 @@ class Configuration implements ConfigurationInterface
         $treeBuilder = new TreeBuilder();
         $rootNode = $treeBuilder->root('wallabag_import');
 
+        $rootNode
+            ->children()
+                ->arrayNode('importers')
+                    ->append($this->getURLs())
+                ->end()
+            ->end()
+        ;
+
         return $treeBuilder;
     }
+
+    private function getURLs()
+    {
+        $node = new ArrayNodeDefinition('pocket_urls');
+        $node->prototype('scalar')->end();
+
+        return $node;
+    }
 }