Some JS

brzydal.js

(function($){

    function formLine(number){
        return "<tr class='config-entry'><td headers='name'>" + number + "</td> \
        <td headers='group'>   \
        <input class='text medium-field' type='text' id='group-name' name='" + number +  ".groupName' value='{$config.groupName}'> \
        </td> \
            <td class='count'> \
            <input class='text medium-field' type='number' id='group-count' name='" + number + ".reviewersCount' value=''> \
            </td> \
        </tr>"
    }

    $("#ra-add-button").on('clock', function(){
        var nextId = $(".config-entry").length + 1
        $('#ra-config-body:last').after(formLine(nextId))
    });

})(AJS.$)

html.soy

<tbody id="ra-config-body">
{foreach $config in $configuration }
    <tr class="config-entry">
        <td headers="name">{index($config)}</td>
        <td headers="group">
        {if $config.groupName }
            <input class="text medium-field" type="text" id="group-name" name="{index($config)}.groupName" value="{$config.groupName}">
        {else}
            <span>Whole users<span>
            <input class="text medium-filed" type="hidden" id="group-name" name="{index($config)}.groupName" value="">
        {/if}
        </td>
        <td class="count">
            <input class="text medium-field" type="number" id="group-count" name="{index($config)}.reviewersCount" value="{$config.reviewersCount}">
        </td>
    </tr>
{/foreach}
</tbody>