Add limit for mistakes

[marceloboeira]

As noticed by me and raised by several people on reddit, and twitter, it's easier to get a higher score by randomly clicking stations quickly than to actually try to play the game, which defeats the purpose.

One idea to solve it, is to limit the amount of mistakes to 3 or 5. However, there are still some questions to be answered:

• How to design that in a simple/understandable way?
• Should we have time AND "mistakes" rules for the game? (Looks like there are too many things to know).