Add a solo experience (bots?)

[norswap]

At first, especially for the tech demo, there will be very few players. To demonstrate the tech effectively, we need a solo experience. This could come in two forms:

• Implementing a bot that will join player's games and play against them using a dummy algorithm.
  • The game right now has no gameplay to speak of, so this bot need not be difficult.
• Implementing a "solo" version of the game contracts that automatically performs the bot's action.
  • We can make this generic by using a bot interface that enable other bots to be written.
  • Maybe the main contract should be modified so that it supports both dual-players and bot modes?

[norswap]

Would strongly prefer the first version, since it's a lot easier to build without interfering with the game's architecture.