0 - Unresponded
<ul>
    <li>Once conversation is accepted, customer message is assigned to operator. So it indicates how many messages operators still have to work on.</li>
    <li>New messages received by system from visitors is set to this status. They remain in this status untill operator. [RESPONSE_UNRESPONDED]
        <ul>
            <li>Operator replies to message by writing response. In that scenario message changes status to (3) [RESPONSE_NORMAL]</li>
            <li>Operator replies to message by choosing No reply required option. In that scenario message changes status to (1) [RESPONSE_NOT_REQUIRED]</li>
        </ul>
    </li>
</ul>