The custom displayer of the "users" parameter of the userlist macro should not force the field name

[mouhb]

On the custom displayer of the "users" parameter of the userlist macro the field name/id attributes are hard coded. The displayer should just forward the parameter it receives (ex : https://github.com/xwikisas/application-task/blob/master/application-task-api/src/main/resources/templates/html_displayer/userreferencelist/edit.vm).