Implement a highscore with local storage

[steadyk]

In order to provide a comparison between participants on e.g. conferences, we want to implement a high score list which e.g. shows a nick-name and the time which was needed to solve all riddles.
It might be sufficient for now to provide a local storage (e.g. via a PersistantVolume with hostPath) which stores the highscore.

#66 might be a predecessor.
A nick-name field could then be placed on the startscreen and the highscore could be part on the end-screen.