Replace hydra:Error with application/problem+json

Since a soon-to-be-RFC for problems in JSON already exist, I think we should replace hydra:Error with it.


https://tools.ietf.org/html/draft-ietf-appsawg-http-problem-01


Opinions?

-- 
Asbjørn Ulsberg          -=|=-         asbjorn@ulsberg.no
«He's a loathsome offensive brute, yet I can't look away»