Control signals: set and ignore flag in header
When we send control signals via VILLASweb frontend (slider, button etc.), the relay will send the signal to other clients via the loopback mode and thereby create an artifact in the signals. We should avoid this by marking control signals with a flag for the category in the header and ignore messages of the category
source in clients.
Later, we may use such
source messages to update modifying widgets on the fly.