Fix access of private router service since Symfony 3.4 (#404)

Services are private by default since Symfony 3.4. Since the router service is still directly accesses in various places it needs to be explicitly marked as `public` to prevent deprecations in Symfony 3.4 and errors in Symfony 4.0.

Author: iluuu1994

src/DependencyInjection/Compiler/SetRouterPass.php

@@ -24,6 +24,7 @@ public function process(ContainerBuilder $container)
         // only replace the default router by overwriting the 'router' alias if config tells us to
         if ($container->hasParameter('cmf_routing.replace_symfony_router') && true === $container->getParameter('cmf_routing.replace_symfony_router')) {
             $container->setAlias('router', 'cmf_routing.router');
+            $container->getAlias('router')->setPublic(true);
         }
     }
 }