Game persistence cache

@matthewhuff89 - Work on the GameEngine, cache set up for game persistence. Views aren't done yet, so displaying a live JSON representation of a game for now after joining a match.
why are you touching `#show`?  Seems like you're working with `#poll`

BTW: @beatrixbetsycarroll worked on this same method in her PR. You're unnecessarily increasing the likelihood of a merge conflict you don't (I think) need.