Dynamic column header title

triple_6

Hi,
Im trying to get column names also from json.
My table :

<table id="example000" class="table table-condensed table-bordered table-hover" cellspacing="0" width="100%">
    <thead>
        <tr>
            <th></th>
            <th>Konto</th>
            <th>Nazwa</th>
            <th>Grupa</th>
            <th>Okres 1</th>
            <th>Okres 2</th>
        </tr>
    </thead>
</table>

JS:

var dt = $('#example000').DataTable( {
                "language": {
                    url: 'assets/global/plugins/DataTables-1.10.12/DataTables/Polish.json',
                    buttons: {
                        copyTitle: 'Kopiowanie danych',
                        copySuccess: {
                            _: 'Skopiowano %d wierszy',
                            1: 'Skopiowano 1 wiersz'
                        }
                    }
                },
                "processing": true,
                "ajax": {
                    "url": "assets/db/sales_reports_data_compare_v2.php",
                    "type": "POST",
                    "data": function ( d ) {
                        d.from_date1 = $('#from_date1').val();
                        d.from_date2 = $('#from_date2').val();
                        d.to_date1 = $('#to_date1').val();
                        d.to_date2 = $('#to_date2').val();
                        d.sales = $('#sales').val();
                        d.klient = $('#klient').val();
                        d.string = $('#string').val();
                    }
                },
                "order": [
                    [1, 'asc']
                ],
                "lengthMenu": [
                    [5, 10, 15, 20, -1],
                    [5, 10, 15, 20, "Wszystko"] // change per page values here
                ],
                "pageLength": 10,
                "columns": [
                    {
                                "className":      'details-control',
                                "orderable":      false,
                            "data":           null,
                        "defaultContent": '<i class="fa fa-plus-square-o"></i>'
                    },
                    { "data": "konto" },
                    { "data": "nazwa" },
                    { "data": "grupa" },
                    { "data": "okres1", "defaultContent": "0.00" },
                    { "data": "okres2", "defaultContent": "0.00" }
            ]
} );

My json data:

{  
   "draw":0,
   "recordsTotal":2,
   "recordsFiltered":2,
   "data":[  
      {  
         "konto":"4065",
         "nazwa":"P.P. ARDMET s.c. Jerzy Sobczyk i Przemys\u0142aw Sobczyk",
         "grupa":"DT",
         "okres1":"450.00",
         "okres2":"450.00"
      },
      {  
         "konto":"4066",
         "nazwa":"MDK Piotr Kraso\u0144",
         "grupa":"DT",
         "okres1":"250.00",
         "okres2":"250.00"
      }
   ],
    "columns":[  
      {  
         "konto":"Customer account",
         "nazwa":"Full name",
         "grupa":"Sales group",
         "okres1":"2016-01-01 to 2016-01-31",
         "okres2":"2016-02-01 to 2016-02-29"
      }
   ]
}

I search whole this forum, API examles and stackoverflow but i can't find any working example how get columns name from "columns" json. Could someone help me with this?
Many thanks!