Add lang and hreflang attributes to the language links of the login page.

Add lang and hreflang attributes to the language links of the login page.

- Adding these attribues should make them easier to interpret for VoiceOver and other assitive technologies.
- This assumes that people will enter the name of the language in the target language to MediaWiki:loginlanguagelinks, which is a convention but not a requirement of course. However I think making the bet that people actually do that is safe enough.
- Switch the name of the old attr variable to query, which better reflects what it is supposed to be used for.

Change-Id: I0cdae9f1e539b9b9c2b99ea1db1ba62bbbb0bdc5