Abstract book for testing

[awfm9]

After moving book back into the network package, testing has become harder because it is now a hard dependency. It would be good to abstract all events that can happen in a handler as its own interface, and inject two interfaces into the handler on start.

Each handler at that point has: log, waitgroup, config, dependencies, events. I would love it if we could abstract the first three into dependencies, but that would be a bit too convoluted of an interface I believe. Go is just not made for this kind of functional programming.

[awfm9]

Has been done in #71