Add new GameHandle class for GameMaster.

This is a very mild code simplification, but mainly I'm doing it
because I want to add per-game ACLs and the previous structure was
a lame way of handling games in the first place.  Eventually this
would presumably have more, but for the time being it's got enough.
Actually track the config filename.

game_master.py was blindly reloading giles.conf because, well, this
wasn't an option until recently.  This was seriously messing up a
major config change I'm in the middle of implementing.  This is still
rather hokey; the right thing now is probably to /just/ pass the
filename and do the right loading thing in server.py or somewhere else,
but it'll do for now.
Change game definitions in giles.conf.

The new method--while more verbose (although not by much)--allows for
specifying on a per-game basis whether or not it is "admin-only."
This still doesn't actually /do/ anything, but will shortly.
Actually use admin-only ACLs in game_master.py.

We no longer allow admin-only games to be instantiated by non-admins.
Do not list admin-only games for non-admins.

It's not fair teasing non-admins with games that they cannot themselves
start copies of.
Allow admin loading of admin-only games.

Now newly-added games can have the admin-only bit set (useful for
beta-testing on a live server).