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
Better to just test `current_user_can( 'edit_comment', $comment_id )`, rather than both, I think.

Why: we test the general permission to see if we should show a menu, etc, but we test the specific permission when testing if we can act on that specific object.