Club now carries its own season_start and season_duration_months,
editable via controlpanel; generate_seasons chains each new season off
the day after the club's last one ends (or its configured start, for a
club with none yet) instead of assuming every club runs Aug 1 - May 31.
Adds --resync to the generate_seasons command to clean up seasons left
over from the old hardcoded rule -- removing any that don't match a
club's current settings and aren't still referenced by real data.
Bernard Siebens
8598fd2b46