Allow comment moderation

[ghost]

Spin off of #2675 .

In cases when the user cannot delete a comment (not the author / formerly the author but comment anonymized / not namespace administrator), it would be good to have an additional button to report a comment to the namespace administrator, for moderation.

An e-mail would then be sent to the administrator with the given recommendations from the user, pointing at the "offending" comment.

Given the very sporadic usage of the feature at large, this is very low priority at the time of writing.