Support Contao 4.9 with missing class tl_settings

[rabauss]

The class tl_settings no longer exists in Contao 4.9, so the callback function should instead extend Contao/Backend!

[fritzmg]

Hm, shouldn't it be either \Contao\Backend or Backend? Aren't all DCA files automatically in the Contao namespace? I am not sure.

[fritzmg]

Also technically, the class should not extend anything at all, as it is not using any features of tl_settings or even \Contao\Backend.

[rabauss]

I just used the extends from tl_article without thinking :-)
But you'r right there is no need of extends!