FLM03: Beside grid voltage also grid frequency as output

The new FLM03 provides the capability to measure phase voltage; this is done along a very neat phase sampling. As for phase shift calculation already the zero-crossings are detected, it would be easy to also provide the corresponding current grid frequency as an output option. This may be fed then into https://netzsin.us/ as an additonal indicator. Everything present, just a matter of a proper mqtt topic, I think...