Move worker, producer, consumer to new directory
Fix process termination

Before, this package was a mess of signal handling. Terminating the
frame consumers did not work correctly and cleanup functions were not
always called.

Instead, the producer is terminated first - no more frames will be added
the queue. The frame queue is the closed. The server blocks until all of
the frames have been processed. Then, the server closes the energy_queue
and blocks until all `RawEnergySensorReadings` have been processed.

Thus, the `FrameConsumers` and the `EnergyConsumers` have been shut down
gracefully. :)
Clarify producer / consumers naming
Fix class names for frame and energy producer / consumer
Improve log messages for shutdown sequence