Allow admins to modify edit notes

In cases where a user either posts links to downloads on an edit note or does something that breaks the CoC and we would rather not leave up (insults to other editors, for example), we should give admins an easier way than direct database editing to modify the offending edit note. This would also be useful for cases where a user, say, copies their name, email address or whatnot on an edit note by accident and wants it removed.

We will need a clear list of things we will remove or edit from edit notes, both on request by the same user and on report by others, and make that list public. This will make sure people don't expect us to come "intrude" in their edit notes without good reason.