WizardBus should not serialize/deserialize in-memory messages

[grepory]

The current MessageBus interface should be replaced as such:

// MessageBus is the interface to the internal messaging system. It must be
// safe to be used by multiple goroutines.
type MessageBus interface {
	daemon.Daemon

	// Subscribe allows a consumer to subscribe to a topic,
	// binding a read-only channel to the topic. Topic messages
	// are delivered to the channel as simple byte arrays. Consumers should
	// use type assertions to convert the incoming messages to a pointer to an
	// appropriate value.
	Subscribe(topic string, consumer string, channel chan<- interface{}) error

	// Unsubscribe allows a consumer to unsubscribe from a topic,
	// removing its read-only channel from the topic's bindings.
	// The channel is not closed, as it may still having other
	// topic bindings.
	Unsubscribe(topic string, consumer string) error

	// Publish sends a message to a topic. Publishers should be sure to pass by
	// reference as this is intended to be used by multiple goroutines.
	Publish(topic string, message interface{}) error
}```

[grepory]

This is going to be a really crappy refactor, and is likely to break any WIP branch anyone has. I'm happy to volunteer as tribute to organize and/or do this work.

[grepory]

Oh yeah you can't assert on non-interface types.