Changes supporting Arabic NER model

[edi-bice]

I built a model for Arabic NER using company resources so I cannot make that one available. Assuming one builds such a model (making use of IOB scheme), these are necessary changes. I will see if I can build a model which does not make use of the company resources.

[westei]

IMO the changes to the default configuration for Arabic would break the language because the models/arabic-ner-model.ser.gz will not be available at runtime.

The additional mappings to the TagSetRegistry can be added for sure

[westei]

Users that need to reconfigure a language configuration can do so by changing the config in the configuration folder of the server. See the Customize the configuration section in the readme

[edi-bice]

OK that makes sense.