server: save game each 2 minutes

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
server: use cPickle

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
server: minor clean up of `server.game`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>