[Publications] Updating the publication form does not change `cf_citation` field

When an editorial administrator changes the DOI of a draft publication object, the citation field is not updated. This is because, even if it is a computed property, it gets manually cached in the database (in cf_citation) at creation time.

We should either:

• force this field to be recalculated every time the form is saved to avoid inconsistencies.
• remove cf_citation and use citation as a true dynamically-computed @property