匿名Group Format
The user can change the group information.
示例：
代码：
<table class="easyui-propertygrid" style="width:300px" data-options="
url: 'examples/propertygrid/propertygrid_data1.json',
method: 'get',
showGroup: true,
scrollbarSize: 0,
groupFormatter: groupFormatter
">
</table>
<script>
function groupFormatter(fvalue, rows){
return fvalue + ' - <span style="color:red">' + rows.length + ' rows</span>';
}
</script>