Tournament mode

[mueslo]

Add option for all local bots (or better: local bots that are marked as being enabled) to be part of a tournament, which would run in the background, and you could check that tab once in a while. The rating scheme would be that of robotgame.org (thanks to bh for this snippet):

K_FACTOR = 32

def new_rating(r1, r2, result):
    expected = 1./(1. + pow(10., (r2 - r1)/400.))
    return r1 + K_FACTOR * (result - expected)