append.c: add username and accountId to annotator dlist

[ksmurchison]

Per a request from @rjbs

Is there a way to do any testing for these fields in Cass?

[elliefm]

Looks like Annotator.pm uses this feature... have a look at new() (sets up annotation_callout option), and start_my_instances() (arranges for utils/annotator.pl to run as a daemon service -- so have a look at that too)

[rsto]

@ksmurchison this PR is still a draft, do you already want my review?

[rsto]

@ksmurchison please add reviewers again once it's clear if to continue with this