Added current_user_can( 'edit_comment', $comment_id ) to ajax moderation functions

- Also enqueuing moderation JS if the current user is author of the post

https://github.com/GigaOM/gigaom/issues/5236
Don't we only want to enqueue on `is_singular()`, then test permissions?

For permissions, perhaps we just want to test `current_user_can( 'edit_post', get_queried_object_id() )` and skip `current_user_can( 'moderate_comments' )`?