A service runner to periodically gather data from disparate sources.
Data Gatherer is built around EventBus.
Data is produced by UpdateProducers, which are periodically executed
by their encapsulating EventBusScheduledService which posts the
List<Sensor> that they produce to the event bus. See
ServiceRegistry for where these are constructed.
Data is sent to EmonCMS by EmonReporter, which is registered with
the event bus.