This is a chat application that allows users with different roles to chat.
User
Users can be logged in and out.
Users can only edit their own comments.
Users cannot delete any comments.
Moderator is a User.
Moderators can only edit their own comments.
Moderators can delete any comments.
Admin is both a User and a Moderator.
Admins can edit any comments.
Admins can delete any comments.
Comments contain a reference to the User who created it (author)