Add support for deletion of Arisa's comments (#488)

[DrAwesome4333]

Purpose

Support the removal of incorrect or redundant comments made by Arisa since staff members can still see the comments after they are hidden.

Approach

Have Arisa delete its own comment if a staff member edits the unwanted comment with a specified tag.

The module will check for recently edited comments that where originally authored by Arisa, staff restricted, and contain the configurable tag _ARISADELETE

The comment deletion was accomplished by modifying the Domain's Comment class to include a removal method similar to that of the Attachment class.

Future work

Checklist

• [x] Included tests
• [x] Updated documentation in README and docs folder
• [x] Tested in MCTEST-146

[CLAassistant]

All committers have signed the CLA.