Mechanism to see which components are online

[oxivanisher]

Should there be a mechanism to see, which components are online?
It could make use of the following things:

• MQTT LWT
• some method to know when a component last communicated to find out if it hangs

[oxivanisher]

Since LWT is already enough, there is probably no need for an additional mechanism.
The LWT is currently not used. I implemented something similar by myself for the LED strips, but in the end i removed this completely. It is better to have old strips around, than to loose still required ones. Also a new way of defining the mqtt client identifier in the d1ws2812mqtt project helped a lot, since strips will get the same id once they return.

The question remains for the other components. With use of LWT, it is very simple to implement this and might be displayed at the same place as the tracker name in #33 .