Update the styles for the header row based on the active filters
function () {
        var me = this,
            headerCt = me.view.headerCt;
        if (headerCt) {
            headerCt.items.each(function(header) {
                var filter = me.getFilter(header.dataIndex);
                header[filter && filter.active ? 'addCls' : 'removeCls'](me.filterCls);
            });
        }
    }