Unregister users when signout

- app/routes/api.js: add registerUser()/unregisterUser()
- app/routes/api/auth.js: move /auth/signout in app/routes/api.js
- LICENCE: add GPL licence
- package.json: update dependencies and project infos

Signed-off-by: Boris HUISGEN <bhuisgen@hbis.fr>