Option to pass virtual pin in message

[xoseperez]

Checking the message for a virtual pin definition allows for a greater flexibility without changing the current behaviour.

I use it to map MQTT topics to virtual pins in a function node and redirect it to a single blynk write node.

[gablau]

I xoseperez, thanks for the contribution, it is very useful, will be integrated into the next release! I think it's useful to add this function to the "set property" node.