Allow ChildProcess to be move-constructed (and prevent copying)
handle_signal(): No need to explicitly kill child process on parent HUP/TERM
ferry/eventloop can take multiple child processes to mind
delayshell: does all ferrying with privileges dropped
Make ferry templated by ferry type
Refactor delayshell into a general packet shell
Rename FerryQueue -> DelayQueue
Add cellshell (copy of delayshell)
Working cellshell