Receiving mentorhelp responses should play a sound

[Caro]

edit: here's one that I came up with that would fit well in my opinion. Two-tone chime ending on a high note to give it a friendly feeling rather than a monotone thing like an admin message that makes you clench.
http://puu.sh/Hv5ZP/e8df81d5ca.ogg

Thanks Virva, I went ahead and PR'd the idea:
https://github.com/goonstation/goonstation/pull/4224