Resolve "Implement DTD XML validation tool in Production editor"

This adds JATS validation to Kotahi – when you generate XML on the production page, it's run through a JATS validator, which will complain if the JATS is invalid for any reason.

There's not a good way to test this on the front end, as the JATS that we're generating from Wax should always be valid – and if it's not, something's wrong on the dev end. The most noticeable effect is that it now takes a bit longer to generate XML. If the JATS is incorrect, you are notified on the front end.

Also in this is a Jest test for valid and invalid JATS; the validate function can be manually fed JATS to see what it comes out with.