New module @turf/center-mean

[muziejus]

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[muziejus]

I couldn't find this function, as turf-center and turf-center-of-mass seem to do different things. A simple (weighted) mean center function will come in handy once I start calculating standard deviations, etc.

[DenisCarriere]

👍 Sweet looks great, however I'm going refactor this as an optional parameter within @turf/center, I'm still going to merge PR to preserve your commit contributions to TurfJS.

Thanks a lot @muziejus ! 🎉