Add a link between accompanying period and user

It is now allowed to indicates who make/made the accompanying period.

This feature may be hidden by a specific configuration option. Default
to visible.

DependencyInjection/Configuration.php

@@ -78,6 +78,12 @@ class Configuration implements ConfigurationInterface
                                 ->append($this->addFieldNode('memo'))
                         ->end() //children for 'person_fields', parent = array 'person_fields'
                     ->end() // person_fields, parent = children of root
+                    ->arrayNode('accompanying_periods_fields')
+                        ->canBeDisabled()
+                        ->children()
+                                ->append($this->addFieldNode('user'))
+                        ->end() //children for 'accompanying_person_fields', parent = array 'person_fields'
+                    ->end() // paccompanying_person_fields, parent = children of root
                 ->end() // children of 'root', parent = root
                 ;