Update framework/web/helpers/CHtml.php

Add some inner "prefix"/"suffix" html code around the label content, without modifying CHtml::$beforeRequiredLabel and CHtml::$afterRequiredLabel

Example source code of how to use
```
echo $form->labelEx($model,'email', array('class'=>'control-label', 'beforeInnerLabel'=>'<i class="icon-envelope"></i> '));
echo $form->labelEx($model,'subject', array('class'=>'control-label', 'beforeInnerLabel'=>'<i class="icon-question-sign"></i> '));
```
It this case we are adding an image <i class="icon-envelope"></i> before the label content "Email"

beforeInnerLabel and afterInnerLabel can also be used if a label don't have the "require" tag.

See produced html code demo page http://shop.glasbuttek.lu/information/contact