Add JSON MIME types to HttpResponse in resolve() per digi604's direction

This fixes an issue where the side frame causes redirects to non-sensical URLs of the type: `http://127.0.0.1/en/<html><body>en</body></html>` or similar.
Merge pull request #2837 from mkoistinen/json_mime_type_for_2788

Add JSON MIME types to HttpResponse in resolve() per digi604's direction