Implement Erlang Monitoring

[Kartstig]

We should take advantage of Erlang's built-in monitoring: http://erlang.org/doc/reference_manual/processes.html#monitors

We can update the process_check macro to use this technique instead of polling each process with Process.info/1. We would have to make another process that runs and just waits on receive until DOWN is given, then sends the information back to the HealthServer, and goes back to waiting.