Support multiple keys per replicator
In some cases, it would be necessary to use replicator keys over multiple keys. This is for example the case with MeteoIO's MeteoBlue plugin: we would need to define together: STATION1=.... STATION1_ID=... STATION1_NAME=...
Currently, we need to define 3 replicators (one per set of keys: STATION#, STATION#_ID and STATION#_NAME). Therefore, they don't appear grouped together. A better option would be to define a STATION# replicator with the others as children.