Change `UserListener` to `App\UserListener`
Change `UserListener` to `App\UserListener`

Renaming `UserListener` to `App\UserListener` so it is clear to unaware users that it is FCQN

Addressing [note](https://github.com/doctrine/DoctrineBundle/pull/1161#pullrequestreview-404907740) from @ostrolucky.
doctrine/DoctrineBundle