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");