Floating Gutter

Just so we have an example of this feature: If the table has a horizontal scrollbar, the checkbox column should stay fixed while you scroll, since this will make it easier to work with selection on mobile phones.

```
$.getJSON('assets/rowdata.json', function(json) {
	ts.ui.get('#table', table => {
		table.selectable();
		table.cols([
			{label: 'ID', minwidth: 300},
			{label: 'Name',minwidth: 300, wrap: true},
			{label: 'Price', minwidth: 300}
		]).rows(json).max(10);
	})
});
```