Invited director registers and etablissement already exists

[kammor]

As an invited director not registered yet When I register myself And my etablissements has already been created Then the etablissement is not created again And I am set as the responsible of this etablissement

• Add prospect id to table etablissements
• Link etablissements to users when the user registers and its etablissement already exists
• Add doctrine/dbal dependency - required to modify columns within migrations (see https://laravel.com/docs/5.8/migrations#modifying-columns )