Server registration config

Ability to specify an optional timeout config for a Server binding to a port.  This is to prevent a Server from staying in a "binding" state indefinitely while the port is unavailable.  Instead, if it cannot bind, the Server actor is killed.  This required a few changes to the WorkerManager and Worker actors, mainly around who watches the Servers for death, and correctly unloads them from the IOSystem.

@DanSimon 
withIOSystem, on shutdown, will now assert all servers are also killed.