Update PredictionModel defaults to average values.
Move worker code from server.js to worker.js
Move master code from server.js to master.js
Schedule sounding for download using Redis

Compute latest and next sounding timestamp. Latest and next sounding scheduled
on init. Schedule is managed using timeouts. When timeout expires, download
queue is cleared and each file is pushed to the queue. Queue is managed using
node_redis. Closes #25