Move user fk from HiiCartBase to concrete subs; only close over hiicart_settings in __init__ methods, so if we want to override them, we only have to do it in one place
Move user fk from HiiCartBase to concrete subs; only close over hiicart_settings in __init__ methods, so if we want to override them, we only have to do it in one place

hiidef/hiicart,hiidef/hiicart,kbourgoin/hiicart