Updated Appliance Versioning

Users who have been using TurnKey for a while, may have noticed that the release cycle of TurnKey appliances has changed in more recent times. Since version 14.2, we quietly implemented a new versioning regime which allows for appliances to released individually, i.e. be on different versions. This allows us to update specific appliances as needed, rather than needing to wait and do them all in a batch. I've been meaning to explicitly share this info for a while now, so here we go...!