Add SKOS relations to JSON-LD serialization

[danmichaelo]

Realized earlier today that skos:relatedMatch is returned as related:Match in the JSON-LD serialization.. example 🌵 Ouch!

As a start, I added a failing test case to document it.

I think the easiest fix is to add the various SKOS mapping properties (exactMatch, closematch, etc.) to the default JSON-LD context). Let me know what you think.

[osma]

Ouch indeed! Thanks for spotting!

A failing test is a great way to report an issue :)

The proposed solution sounds good. I think this will only affect skos:relatedMatch since it's the only property whose URI starts with another SKOS property. But defining all the SKOS mapping properties is better for clarity and consistency.

[danmichaelo]

Ok, added the mapping relations to the context for the data endpoint.

I also wanted the output from the search endpoint to be more consistent with the output from the data endpoint, so I added any additional fields being requested using the fieldsparameter to the JSON-LD context there. Note that this change is technically breaking (if users just rely on the 'skos:' prefix being present in the keys in the resulting JSON without taking the JSON-LD context into account), but I guess the impact should be low since it only affects additional fields requested using the fields parameter.

[osma]

Excellent work! I see you even added a RestControllerTest class, which we didn't have before.

The only problem I see is that the Travis tests failed due to an unrelated PHP version compatibility issue. That should be fixed in master now. I will try merging this first into a separate branch to make sure it doesn't actually break the tests.

[osma]

Tests OK after merge. Thanks a lot!