Improve json-ld representation of events
requested to merge linos/gancio:fix--better-spec-compliance-with-activitystreams-and-json-ld into master
- Specify the type of the location object: "Place" as found in https://www.w3.org/TR/activitystreams-vocabulary/#dfn-place
- Extend the object via the schema.org/address with type text as we currently a single text field is used