FRED needs authentication

Hi there,

when I'm attempting to link entities using FRED the there is a 401 not authorized error risen:

```
2020-11-13 15:51:23,926 [pool-1-thread-2] ERROR [org.aksw.gerbil.annotator.decorator.ErrorCountingAnnotatorDecorator] -
```
As the [official API documentation says there is an authentication token required.](http://wit.istc.cnr.it/stlab-tools/fred_api/). As neither the `annotators.properties` file nor the wiki does mention this auth token, I suppose it's a recent change by the developers of FRED and not implemented by the current version of GERBIL?

Best,
Marco