bug: Handle switching output/device removal

[mman]

When Shelly RGBW disappears from the network, the /Status goes from 9 to 32, and eventually the switchable device and its output disappears from the MQTT tree.

Handle this properly.

[mman]

As suggested each switching device (and other devices that may expose switchable outputs in the future) exposes /Connected path. But from my current testing experience, for example Shell devices disappear without ever setting connected to anything else than 1. So not a viable path to detect device removal.