REST API returns HTML for 404 and other errors #1859
Description
Describe the bug
Currently our API sits behind nginx, which means any errors such as 404 will return a HTML error page. This is somewhat awkward, as the rest of the API is in JSON. For consistency we should improve the error page.
At the very least it should consistently return an application/json file for errors, and as a stretch goal we can do what Django REST server does and use accept to distinguish between API users and browsers, and show a nice HTML error page only if the user is visiting the page using a browser.