Add per-camper "Thank You" rate limit

[SaintPeter]

No more than X Thanks Yous per minute/hour/etc. Also, maybe no more than ?10? per thank you. Don't award any points at all if there are more than a certain number of @mentions in a message?

We had an issue where someone came into the main channel and spammed thank yous A LOT. It took a long time for Camperbot to process them all and could have acted like a DOS to the API and Camperbot.

[BerkeleyTrue]

@SaintPeter A debounce on a per user bases would work magic here

[raisedadead]

Close as done? @BerkeleyTrue

[BerkeleyTrue]

@raisedadead Is it done?

[raisedadead]

Sorry my bad, I figured it was the other way round. We do see the bot not accept thank yous to same receiver in an hour. Here we want to limit the no of requests a sender can make.