Allow users to delete their own comments / Allow namespace administrators to moderate (delete) comments in their NS

[ghost]

As the title implies, there doesn't seem to be any functionality implemented to delete comments (the closer thing is comment anonymization when a user deletes their account).

It would be a good improvement to allow users to delete their own comments, and namespace admins to do the same for all users in their namespace.

Aside from the self-moderation capability, that would also make it easier to fix privacy issues, e.g. if private data has been put in a model comment by mistake.