for Fargo.io: adds a checkbox to a headline that has no icon; if the icon is "check-empty" it changes it to "check"; if the icon is "check" it makes the headline a child of the last headline in the outline and then collapses that parent headline

todo

todo
	var value = op.attributes.getOne ("icon");
	if (!value) { 
		op.attributes.setOne ("icon", "check-empty");
		}
	else if (value == "check-empty") {
		op.attributes.deleteOne ("icon");
		op.attributes.setOne ("icon", "check");
		}
	else if (value == "check") {
		op.reorg (down, infinity);
		op.reorg (right, 1);
		op.go (left, 1);
		op.collapse (); 
		}