Come up with a game serialization format

[eaceaser]

we need a serialization format for game state in the DB. I wonder if it makes sense to just use SGF? Parsing it is probably a pain tho. So in that case, we probably want to come up with another serialization format.

We could also possible have to serialization formats:

1. One which contains game history and branching. This one is closer to SGF.
2. One which contains just the live state of a game, used for playing and recovering game state.

[eaceaser]

For live games, storing a serialized move list (either in redis or the DB) would be sufficient.

For completed games and reviews, we'll need a serialization format with branching and the like.