Publicationform widget updates

Implements the updated design for the publicationform.

This PR needs a Hilary counterpart to:
* remove the Cambridge Addendum field (https://github.com/CUL-DigitalServices/avocet-hilary/pull/56)
* allow the acceptanceDate field to be cleared in a publication update (https://github.com/CUL-DigitalServices/avocet-hilary/pull/57)