Update TüNews API client

[svenseeberg]

The API structure of tunewsinternational.com changed. Due to these changes new articles are currently not being synced into the Integreat app.

Instead of categories the site now uses Polylang to manage languages. Additionally, there is a custom Integreat field that indicates if an article is relevant for the Integreat App.

According to the Polylang API docs it should be possible to filter languages with a GET parameter:

http://tuenews.de/wp-json/wp/v2/posts/?lang=de

However, the Integreat custom field is not visible(?) in the API. There is an acf attribute, but it seems to be empty in all cases that I checked.

After the API has been fixed, we may have to prune the database on the django-tunews.tuerantuer.org and re-fetch all articles.

[Upacesky-26]

Custom fields are now exposed via the Wordpress API

[svenseeberg]

Awesome, thanks.

So posts can have an "acf:" {"integreat": true} attribute.