marks the sorted column with arrow (asc/desc) in the header
| column_id | string | optional, the column ID |
| direction | string | optional, the sorting direction: "asc" or "desc" |
| preserve | boolean | optional, instructs to preserve previous sorting marker |
dtable = webix.ui({view:"datatable", ...})
dtable.markSorting("title", "asc");
dtable.sort("title", "asc");
dtable.markSorting("title", "asc");