Support Symfony2 2.6 setFactory syntax

[Haehnchen]

factory_class, factory_method = old syntax. support new one

The new setFactory() method was introduced in Symfony 2.6. Refer to older versions for the syntax for factories prior to 2.6.

New:

services:
    newsletter_manager.factory:
        class: NewsletterManagerFactory
    newsletter_manager:
        class:   NewsletterManager
        factory: ["@newsletter_manager.factory", createNewsletterManager]