Filter and Cancel submit button labels double translations

[LiborSitek]

Hi, labels on submit buttons 'filter' and 'cancel' in filter form are being translated twice - manually in the form and then automatically when rendering. I guess
#437: $form['filter']->addSubmit('filter', $this->translate('Filter'));
#440: $form['filter']->addSubmit('cancel', $this->translate('Cancel'));
should be
$form['filter']->addSubmit('filter', 'Filter');
$form['filter']->addSubmit('cancel', 'Cancel');
in Datagrid.php