utilize archived field for season

[blaskovicz]

Features

• ability to toggle archived on and off from season manage page
• archiving a season hides it from the season list page
• allow extending due date
• if archived, disallow any modifications to the season (except unarchiving)
• disallow unarchive unless extending the date past now+1day or something
• auto-archive season after end date
• notify owner of impending end + option to extend
• notify users of season end
• send out season results after end date?