Consider tuned-group-by equality semantics

[rbrush]

As brought up at https://github.com/cerner/clara-rules/issues/393#issuecomment-397525366, there is a potential bug if the tuned-group-by function uses Clojure records as the key. This isn't the case for all current usage within the system so there is no observable bug right now. This is simply be logged to track discussion and consideration.