CE-1103 Enable WikiaInYourLang extension on all wikias

Per Yoko request the WikiaInYourLang extension is going site-wide. That requires a tweak that retrieves "vanilla" domain of a wikia without its language prefix (e.g. retrieves pad.wikia.com from zh.pad.wikia.com).

Corresponding config PR: https://github.com/Wikia/config/pull/756
Looks like a piece of code waiting to be unit tested :)