Move wfMsgExt to wfMessage

* Move wfMsgExt depeciated in MW 1.21 to wfMessage
So this is it:
```php
$emailText .= '<h3> ' . wfMessage( 
			'swl-email-changes',
			$changeSet->getEdit()->getTitle()->getFullText()->rawParams(
			$changeSet->getEdit()->getTitle()->getFullURL()
			)->escaped() . ' </h3>';
```