Reduce ServerChild-ServerManager coupling

The tasks of re-launching and cleaning up ChildServer instances should
be contained within the ServerManager's logic.
Extend ServerManager to emit process identifiers
Add module for persisting PID data
Manage child processes
fixup! Manage child processes
fixup! Extend ServerManager to emit process identifiers
fixup! Add module for persisting PID data
Merge pull request #122 from jugglinmike/cleanup-procs

Cleanup procs