Added the ability to bind ajax js to a class

Example:
```
<div class="issue-buttons">
<?
echo CHtml::ajaxButton('Start', $this->createUrl('status', array('id'=>$issue->id, 'status' => Tasks::STATUS_START)), array(
                'type'=>'POST',
                'data'=>array('update'=>true),
                'update' => '.issue-buttons',
            ), array('class' => 'action-buttons', 'bindClass' => "action-buttons"));
?>
</div>
```
And we have js:
```
jQuery('body').on('click','.action-buttons',function(){jQuery.ajax({'type':'POST','data' ...
```
	modified:   framework/web/helpers/CHtml.php