[Routing] Added an extension point for globals in AnnotationClassLoader

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

We need to add a new extension point for global to be able to support
`@Method` on class:

``` php
/**
 * @Route("/api")
 * @Method("GET")
 */
class FooBarController
{
    /**
     * @Route("/")
     */
    public function showAction()
    {
    }

    /**
     * @Route("/new")
     * Method("POST")
     */
    public function newAction()
    {
    }
}
```