Problem: disconnecting requires access to CharacterSaver,
which is not available in Client.
Having it in a service like this solves that problem.
Next step is to migrate all calls to Client#disconnect and Client#forceDisconnect
to their TransitionService counterparts.
Preparing for change in Command#handle,
which is going to take a CommandContext as an additional argument.
This way we can pass in command dependencies in a safe way
instead of requiring them to access static methods.
NoteService should be the only class with access to NoteDao;
nowhere else should NoteDao be accessed directly.
Channel dependencies are static in PacketProcessor, for now.
Ideally they would be injected in the constructor,
but since the constructor is private and I don't want to open
up that can of worms, I'll leave it like this.
At the very least, now we have a way of injecting services into
the handlers. This will make further restructuring way easier.
