Don't display sensitive data to users when not being able to connect to the API

When the API Damon is not available, schleuder-web displays currently the following to users

Cannot connect to the Schleuder API.

Please check if it's running at https://some-host:4443/ or
change the settings in /var/www/schleuder-web/config/schleuder-web.yml.

Imho this is too much data that is only relevant to admins and should not be displayed to users.

Users should get a nice message explaining that the service is temporarily not available (and they should contact their administrators?) and log the upper info only in the logs.