[All games] Add bots for all games

[vdfdev]

Being able to play single player games is a large use case for lots of users. So it would be nice if all games had single player bots.

Games missing AI:

• Nine mens morries (easy to do)
• Reversi (easy to do)
• Cornerus (easy to do)
• Take 6 (harder)

[vdfdev]

This section might help: https://boardgame.io/#/tutorial?id=adding-ai

But it seems like the bg.io implementation is not really well documented and there are more functionalities than that.

[spollard]

Looks like Reversi has an AI implemented already

[JosefKuchar]

@spollard It's just a random bot, but yeah you are right