No ability to set default checked fields in Grid->addSelection()

[DarkSide666]

Is there ability to select some of checkboxes on page load of $grid->addSelection() ?
I couldn't find it. Would be very good to have and probably not that hard to implement.

Probably the nicest way would be to pass string or array of selected checkboxes as argument:

$grid->addSelection(['foo', 'bar']);
// or
$grid->addSelection('foo,bar');

[mvorisek]

related/selection with #1877