adding introduction to citing author and citing work

[acholyn]

closes #383

[tcouch]

When adding or updating an introduction on a citing_work or citing_author, if it includes a mention of a bibliography item, you get the following error:

File "/app/rard/utils/basemodel.py", line 319, in link_bibliography_mentions
     for ant in antiquarians:
UnboundLocalError: local variable 'antiquarians' referenced before assignment

We can't really assign an antiquarian to a citing author or citing work, but we would like to link bibliography items in the same way. We'll have to expand the link_bibliography_mentions method to handle this.

[tcouch]

If you look at the Antiquarian detail page, there's a htmx trigger on the bibliography item list which refreshes it when the introduction is updated. It just means you get to see the updated bibliography without having to refresh the page.