game: Add support for a static "meta" field to hold game metadata

We use a static getter/setter function for this since JavaScript
doesn't yet have wide support for static fields.

Also, we duplicate the data on both a field within the class itself
(Game._meta) as well as in the prototype (Game.prototype). The purpose
of this is so that we can access this meta-data as either a class
static (Game.meta) or via an instance (some_game.meta).