Move wfMsgExt to wfMessage

* Move wfMsgExt depeciated in MW 1.21 to wfMessage
Before I confuse this even more. Is this what is meant?:
```php
$emailText .= '<h3> ' . wfMessage( 'swl-email-changes' )->excaped(),
		$changeSet->getEdit()->getTitle()->getFullText(),
		$changeSet->getEdit()->getTitle()->getFullURL()
		)->escaped() . ' </h3>';
```