Figure out better way to slow down messages

[stevenewald]

At full speed with many bots, the exchange can easily send out more information than algorithms can process. This can be megabytes of messages per second, meaning hundreds of thousands or millions of callback calls. For the competition, this was fixed by artificially slowing the exchange a bit. We should find a better solution.

There will always be cases where user-callbacks may be too slow (while True), so we can't just wait for them all. This is a design problem, not a technical one