Validate class name when generating contributions

[Koc]

https://github.com/sergeil/ExpanderBundle/blob/1.0/Generation/StandardContributionGenerator.php#L46

Please specify bundle # you want to contribute to: 29
Please specify a contribution class name:
Done!
 - New file: /var/www/src/Modera/BackendOnDemandRegistrationBundle/Contributions/.php
 - Updated: /var/www/src/Modera/BackendOnDemandRegistrationBundle/Resources/config/services.xml
dev@dev:~/modera$ mcloud run php. "app/console sli:expander:contribute modera_routing.routing_resources"
Using folder name as application name: modera

No key found - fallback to no-ssl


  [Symfony\Component\DependencyInjection\Exception\InvalidArgumentException]
  "'Modera\\BackendOnDemandRegistrationBundle\\Contributions\\'" is not a valid class name for the "modera_backend_on_demand_registration.contributions." service.