At present, mounted controllers can get weird route names. For instance, let's
say you have this controller definition:

    $otherController = $app['controllers_factory'];
    $otherController->get('/{name}', function (Request $request, $name) use ($app) {
      return new Response("Goodbye $name!\n", 200, ['Content-Type' => 'text/plain']);
      });
    $app->mount('/goodbye', $otherController);

The generated route name in this case will be `_goodbyeGET_name`, which
technically contains everything, but is ugly.

With this PR, the route name will change to `GET_goodbye_name`, which is
considerably easier to parse when debugging.