finish generation of json-ld context file

[kurzum]

There are the following todos:

1. add extra prefixes in the template at https://github.com/NLP2RDF/software/blob/master/java-maven/tools/src/main/resources/json-ld-context
   Actually I would not recommend using prefixes. They are difficult to resolve. especially for objects. Let's remove them, unless you find some practical use for them
2. add datatypes for datatype properties on line 21 https://github.com/NLP2RDF/software/blob/master/java-maven/tools/src/main/resources/json-ld-context#L21
   this causes a JSON syntax error currently . There is some #if #end template work needed, but Velocity is well documented: http://velocity.apache.org/
3. same for classes and maybe individuals, if needed
4. We need to use the latest nif-core ontology, version 2.1
5. if we have the json file, we can upload it to persistence.uni-leipzig.org and include