Synchronize application shutdown closing Run methods when broadcast channels are closed

[andig]

This PR addresses the following points:

• make rate limiting reusable by moving from MQTT output to scheduler
• synchronize application shutdown by making tee wait for attached consumers to shutdown
• have all tee consumers valididate input channel still open or close if not
• finally use these to allow homie to unpublish retained messages when sdm is shutdown

Clean version of #102, replaces #89