Add support for CKAN servers that do not support CORS handling

[robbieaverill]

Browser: Chrome 71 on macOS

If you type an invalid data.govt.nz URL into the resource locator field, you get this console error:

Access to fetch at 'https://catalogue.data.govt.nz/api/3/action/package_show?id=directory-of-educational-institution'
from origin 'http://ss43.localhost' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present 
on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the
resource with CORS disabled.

I suspect it'll be better to handle this from our end (support CKAN servers that don't provide correct CORS headers) than to expect that they all will.

On a side note, we also get a 404 error from the failed network request in the console too. Ideally we'd handle this gracefully so CMS users won't end up with set of console errors.

cc @camfindlay