Limit the Karma modification per user, per day

I use this bot a lot on a channel. No limit to the fact that anyone can modify the Karma of an object any number of times is something of a bug. As users changing and spamming Karma object without limit is highly probable and that makes the concept of a Karma object, useless.

I'm including a patch, that fixes the problem by limiting the Karma modification of a term only once per 24 hrs per user. Please consider including it in the next release of bot.module and making further improvements in this patch.