Implement bidding library (port bidcat)

A library for collaborative, auction-like bidding needs to be implemented.

The requirements are the same as for the old codebase. Therefore it's probably sufficient to port the previous implementation called ["bidcat"](https://github.com/TwitchPlaysPokemon/bidCat/blob/master/bidcat/__init__.py). It's documented pretty well, so check it out to know the specifics.