Allow clients to request expanded, compacted and flattened representation

[dschulten]

The media type application/ld+json defines three profiles [1] which allow clients to request expanded, compacted and flattened formats (terms become urls)

[1] http://www.w3.org/TR/json-ld/#application-ld-json

Makes it easier for clients to work with the responses if they need the full URIs.