(CE-717) Fix or remove incompatible methods in language library

* Fix fetchLanguageName by removing the inLanguage option due to
  its reliance on a method that is not supported in MW 1.19
* Remove isSupportedLanguage and isKnownLanguageTag due to their
  use of methods not available in MW 1.19
* Fix formatDate to use wfTimestampNow instead of the MWTimestamp
  class which is not available in MW 1.19
(CE-717) Fix bug in mw.language:gender
Merge branch 'CE-717-scribunto-support' into scribunto-support