i18n: consistency tweaks

* replace "article" by "page"
* replace single-quotation by double

Partially spotted by Siebrand
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Gettingstarted-task-copyedit-toolbar-description/en

Change-Id: I1468d1fb63d4f112e8ba81aea59f380f6b5bd322