Consistency tweaks in preparation for adding extension to translatewiki.net

* Set extension credit type 'other'
* Remove 'description'. Not needed when 'descriptionmsg' is set
* Use array for more than 1 author for proper i18n
* Fix URL
* mediawiki -> MediaWiki
* Use template for qqq

Change-Id: I052eb01f024842d7a0de68c6e3d6421f4da8641a