sonata-admin integration

Two admin classes for `Group` and `User`.

    fos_user:
        use_sonata_admin: auto # true, false

Yes, I know, that there is also the `SonataUserBundle`, but it "does too much" and it isn't compatible to `FOSUserBundle` 2 anyway. So I ended with my two custom `Admin`-classes and thought, that it may fit into `FOSUserBundle` directly. It is completely optional.


Sidenote: I was able to provide the translations for english and germany only :wink: