(as discussed in the call) - contributes to #1

Just a note: We do not use eta for JabMap, because we do not want to have a whole JavaScript templating engine shipped with JabRef. We can work on this if users want to, but for now, we should "hard code" a "good enough" JSON. Currently, our only consumer is JabMap - and we should create the subset suitable for JabMap (and still be compatbile with BBT)