Remove Bookkeeper mutexMap

The mutexMap in Bookkeeper is used only for feedback. This removes it in favour of mutexes in the feedback classes.

There are signs of this being done originally, but I can't see why it wouldn't work. I don't think there's a need to have two feedback loops running at the same time with the same mutex?

It might be better to change this straight into a Clipboard, I suspect that using a mutex like this might be undefined behaviour (lock and unlock in different threads).