Add --DB_delete option to clear out the sqlite3 tables of prior_cleaned

[r3m0chop]

prior_cleaned is obtained via:
prior_cleaned = self.audit.get(e, study_uid_pk=study_pk))
and is used to retain the same anonymized values (e.g., Accession Number 7, etc.).

However, any newly generated clean values, as from:
cleaned = str('%s %d' % (e.name, self.audit.get_next_pk(e)))
need a way to clear out the DB of old values from previous incarnations of that line, such as those from the current/soon-to-be-previous:
cleaned = ('%s %d' % (e.name, self.audit.get_next_pk(e))).encode('ascii')