FOR COMMENTS: WIP for cnxml to html on publish

Note: This pull request is not for merge.

`plpydbapi` is a python package that implements the python db api (db connection and cursor) from plpy.  I'm hoping to use this to call cnx-upgrade `produce_html_for_module`.  It's not going to work in this trigger as module_files inserts can only be done after we get the module_ident from the module insert. (right?)

When a module is republished:

1. I insert new rows into `modules` for the collections that the module is part of with an updated version.
2. I copy the collection tree with modified documentid.

Is that all we need to do?