Display organizations as linked objects

[Rikuoja]

Currently, organizations (/v1/organization) are not displayed in the event API endpoint with the JSON-LD notation. Organizations are referred to with pure id (not inlined), which means they cannot be included with the ?include=publisher parameter.

This, of course, is due to organizations being added late to the mix, after API version 1 was published, so it was impossible to change the field format.

Something to think about for v2.

[Rikuoja]

This would have come in handy for City-of-Helsinki/linkedevents-ui#433 and in the future for any event listings.

[Rikuoja]

Also, consider whether also data_sources should be exposed in the API, and serialized the same way?