Extend configuration

Attempt to fix build that is related to configuration as a backside effect there was introduced new configuration property exclude. It allows to set a list exceptions that should be not passed to rollbar. Example:

• Form validation exceptions
• Debug exceptions

symfony_rollbar:
        enable: true
        exclude:
            - \Symfony\Component\Debug\Exception\FatalErrorException
            - \AppBundle\Exceptions\MyAwesomeException
        rollbar:
            access_token: 'some-secret-token-here'