Add full-stops & fix quotation marks

Spotted by Siebrand
http://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Echo-email-footer-default-html/en
http://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Echo-email-batch-body-intro-daily/en
http://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Echo-email-batch-body-intro-weekly/en
http://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Notification-mention/en

Change-Id: Ia1c61c4f78f7b93343ba1174b7446829c216cbfa