Guess template name based on declared method name when using @Template

Stumbled upon this while developing on OS X which has a case-insensitive filesystem. For various non-obvious reasons I ended up calling a controller action using `mycontrollerAction` instead of `myControllerAction`.

Since I was using the `@Template` annotation without any parameters, the template name was guessed, but the guess was based on what I called the controller as, not the actual controller method name, resulting in `mycontroller.html.twig` instead of `myController.html.twig`.

This of course worked fine locally, but failed when pushed to our staging server (which has a case-sensitive file system).