Remove drag disabled rows on moving drag enabled

Qt::ItemFlags TreeModel::flags(const QModelIndex &index) const
{
    if (!index.isValid()){
        return {};
    }

    Qt::ItemFlags result = Qt::ItemIsEnabled |
            Qt::ItemIsSelectable;

    if (!index.parent().isValid()){ // Group nodes can accept drop
        result |= Qt::ItemIsDropEnabled;
    }
    else{   //leaves can be draged
        result |= Qt::ItemIsDragEnabled;
    }

    return result;
}