Dice bot

I wrote a DiceBot that makes dice rolls based on your CommandBot. It currently can make general purpose dice rolls like "3D6" and Shadowrun 3 success tests.

I had to make some changes to your code to make this work and I am not sure if there are no side-effects on other bots so please review my changes. There were two major issues.

* I had to deactivate handling of voice data because the command bot would hang in an infinite loop every time some voice data was received.
* I had to remove CommandBot's channel and prefix filters. I just didn't seem to get them to work properly.

If you want to suggest improvements, feel free to contact me. :-)