Add configs for JSON-LD (`.jsonld`) files

Ensure that clients interpret the content of `.jsonld` files correctly
by serving them with the `application/ld+json` content-type.

Also, ensure that `.jsonld` files aren't served with any of the `html`
related headers, but are served compressed, and their character encoding
is UTF-8.

See also:

  * http://json-ld.org/
  * http://json-ld.org/spec/latest/json-ld/A
  * http://www.w3.org/TR/json-ld/
  * http://www.iana.org/assignments/media-types/application/ld+json
  * https://github.com/json-ld

Ref:   h5bp/server-configs-apache#17.
Close: h5bp/server-configs-apache#17.