Update Template Path notation: FooBundle:B:C.html.twig -> @Foo/B/C.html.twig

[weaverryan]

Where we still refer to a template inside a bundle, we need to update to use the @Foo/B/C.html.twig template. This syntax has always worked, though I think it might only work for Twig (if that's true, we should keep the old syntax only for PHP templates).

Also see: symfony/symfony-standard#861 (comment)