Improve namespace declaration parsing

[dgarijo]

As shown in https://stackoverflow.com/questions/65480889/extracting-ontology-namespaces-prefixes-with-owl-api, there is a native method to retrieve all namespaces.

The method public void loadNamespaceDeclarations(OWLOntology o) in Configuration.java loads the namespaces into a hashmap. However, this is a little redundant, since the following already returns all ns:

Map<String, String> map = format.asPrefixOWLDocumentFormat().getPrefixName2PrefixMap();

Should take the existing map and modify the preferrednsPrefix, instead of re-parsing everything again.