Modified db-prefill to use `fork()` to start up an instance of the API and persona-faker servers, then kill them on completion; this means that we can now run db-prefill without any prior setup (after `npm install`).

This makes use of redis pub/sub to detect when the API and persona-faker servers are set up, so it requires each to send a message after launching their HTTP server so that db-prefill can begin the pre-fill process. If you have already run `npm install` with persona-faker, you will need to run `npm install` again to receive this change on persona-faker.
Prefix stdout / stderr of child processes with their respective names in db-prefill
Cleanup
Setup exit handler before calling startServers so that if we crash for some reason after creating one server but before finishing the other, we can still kill the server that we had already started
Moved startServers to its chronological location, and refactored the server ready listening into a promise with a timeout handler for easier debugging
Changed stdout / stderr prefixing to use a proper stream.Writable subclass; style fixes
Reorganized imports
Merge pull request #88 from cvan/automate-prefill

Enhanced db-prefill to spawn its own API and persona-faker instances