Make Panopoly Widgets translateable

I've found 4 not translateable strings in the panopoly_widgets/panopoly_widgets.module:

$subtype['title'] = 'Add submenu';
$subtype['title'] = 'Add content item';
$subtype['title'] = 'Add content list';
$form['reusable']['category']['#value'] = 'Reusable Content';

This strings should be wrapped into the t() function (like the others in the panopoly_widgets.module).