people can now authenticate via email or unit_code

access code is mapped to a particular user ID card__done
remove scam users (people with access codes that doesn't belong to them)__done
access code expires every day by 12 midnight __done
access code is generated by admin __done

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excos can't see admins (they can only see users(in their unit, that they created)) __done

when people register they use their exco code __done