fix(LabelAnnotator): Added code to clear the default properties if properties are defined in the config file.

[rombaum]

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I fixed the issue https://github.com/EBISPOT/ols4/issues/853 by adding a line to the corresponding Java class LabelAnnotator. As an test I indexed two ontologies. For RadLex I used the following line at the config file for the label "label_property": [ "http://radlex.org/RID/Preferred_name"] . For the second ontology I didn't defined any property for the label in the config file. For RadLex http://radlex.org/RID/Preferred_name was used and for the other ontology the default property rdfs:label was used. The indexed ontologies looks as expected. I used in my case just the Plasma Ontology since it is not so huge and I know that it uses rdfs:label for the labels.