public function addTableColumn($key, $title, $sortable = false, $contentCallback = false)
    {
        $this->tableColumns[$key] = $title;

        if ($sortable === true) {
            $this->tableSortableColumns[$key] = $key;
        }

        if ($contentCallback !== false) {
            $this->tableColumnsContentCallback[$key] = $contentCallback;
        }
    }