Json-LD compatibility

[chriskapp]

We should think about making our specification compatible to Json-LD basically this would mean that we use the @type and @id properties instead of out type property. It could make it a bit easier for developers to process since they could use existing Json-LD libraries and it would be possible to reference the types from the specification in the complete Json-LD ecosystem. Note this would only means that our specification is Json-LD compatible the JSON data which we describe with this specification is complete independent of Json-LD.