Support multiple connected sensors in HA

[infeeeee]

Multiple connected sensor related changes from #96

I separated from there, because this is also needed for brightness as light, lights need custom topics for state and brightness.

A working implementation of brightness as light is on my branch brightness-light. Compare with this branch #124

Difference from #96:

• You can override any topic in entities.yaml, with state_topic_key, command_topic_key options.
• You can have a list as override topic.
  • This is for HA-light, it needs both brightness_command_topic and command_topic. On command_topic HA only sends 0 as OFF payload, ON payload only sent on brightness_command_topic. The problem with this, after callback, it would send the same callback value to both connected sensors. I solved it by sending through valueformatter, so we can filter and modify the wrong values. To understand this better, see the Brightness as HA light #124 , I will document this somewhere. (I also started rewriting valueformatter to make this more easier...)

[richibrics]

Sorry for the delay