User ID for author instead or additional to username

[guidol-ive]

A page has the structure:

<?xml version="1.0" encoding="UTF-8"?>
<hypha type="peer_reviewed_article" multiLingual="off" versions="off" schemaVersion="1">
  <article status="published" author="john" created_at="t1542699796" published_at="t1542705868">
    <content>
      ...
    </content>
    <context>
      ...
    </context>
  </article>
  <discussions>
      ...
  </discussions>
  <approves>
    <approve xml:id="id5bf3bdfc26fcb" user="5ad6f6a7ca858" created_at="t1542700540"/>
      ...
  </approves>
</hypha>

The approval uses a user ID like "5ad6f6a7ca858" to refer to a person. However, the author uses the natural / business key of the users like "john" in this sample.

Suggestion is to use the user ID instead of the user name to refer to the author from the <article>.

This makes updates easier.

[guidol-ive]

In for instance pages/61c30c98432ab, the full name of the author is contaiend in author.