add configuration for user_group table name

DependencyInjection/Configuration.php

@@ -31,6 +31,12 @@ class Configuration implements ConfigurationInterface
         $rootNode
             ->children()
                 ->booleanNode('security_acl')->defaultValue(false)->end()
+                ->arrayNode('table')
+                    ->addDefaultsIfNotSet()
+                    ->children()
+                        ->scalarNode('user_group')->defaultValue('fos_user_user_group')->end()
+                    ->end()
+                ->end()
                 ->arrayNode('class')
                     ->addDefaultsIfNotSet()
                     ->children()

DependencyInjection/SonataUserExtension.php

@@ -86,7 +86,7 @@ class SonataUserExtension extends Extension
             'targetEntity'    => $config['class']['group'],
             'cascade'         => array( ),
             'joinTable'       => array(
-                'name' => 'fos_user_user_group',
+                'name' => $config['table']['user_group'],
                 'joinColumns' => array(
                     array(
                         'name' => 'user_id',