specifies the CSS class that will be applied to a cell of the view
| evs | array | an array of objects of events contained in a cell (defined only in the 'cell' mode) | 
| date | Date | the date of a column | 
| section | object | the section object | 
Available only in PRO Edition
scheduler.templates.timeline_cell_class = function(evs, date, section){
    return "";
};
The template requires the timeline plugin to be activated.