user = {
    id: ObjectId,
    name: string,
    password: hash,
    created_polls: array of poll ids,
    created_answers: array of answer ids
}

poll = {
    id: ObjectId,
    question: string,
    answers: array of answer ids,
    votes: number,
    created_by: userid,
    answered_users: array of user_ids
}

answer = {
    id: ObjectId,
    value: string,
    poll_id: pollid,
    votes: number,
    created_by: userid,
}