Automatically injected url parameter should be optional if they have a default value

[DerManoMann]

Url parameter extracted from the silex url pattern; ie {id} should be flagged optional if the corresponding controller parameter has a default value.

Example:

    /**
     * @SLX\Route(
     *   @SLX\Request(method="POST", uri="/foo/{id}")
     * )
     */
    public function foo(Application $app, Request $request, $id = null) {