added support for cleaning up discourse after edits

This PR does a few things to keep text_discourse clean after edits:

Deletes rows in text_discourse that are associated with rows being deleted in text_epigraphy
Recursively deletes parents that are childless when deletions occur
Inserts new discourse rows in the correct position (using neighboring parents)
Increments discourse units as needed when inserting new discourse rows
Cleans up all discourse iterators after each edit

oaregithub / oare_mono