Initial Scribunto backport

Working from the version that still supported MW 1.20. Required
backporting some parser changes.
(CE-714) Backport handling invalid keys in Lua-to-PHP calls

Backport patch to handle invalid keys in Lua-to-PHP calls for LuaStandalone.
Remove ContentModel reference in SiteLibrary
(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
(CE-723) Add initial support for Scribunto console to Oasis
Merge branch 'CE-723-scribunto-support' into scribunto-support
Remove one of the backported core changes
Add Wikia change comment to backported changes
Add mw.html Lua library
Merge branch 'CE-721' into scribunto-support
Merge pull request #3415 from Wikia/scribunto-support

(CE-711) Scribunto support