Zero warning page fixes

* Cleaned up Zero warning page (visiting zero without carrier support)
* PageRenderingHooks::isZeroSite is now non-static
* Process lang links rewrites only when the zero is actually enabled,
not when X-CS was set by the varnish (which might be in more cases)
* PageRenderingHooks::getWikiInfo now returns an array of 3 elements:
  languagecode, subdomain, site -- just like parts of the current URL,
  and it is no longer static
* getConfig() can now return config if the user is from a zero network,
  but visits a non-whitelisted site/language.

Change-Id: I0abdc13af4e2b85aeb27ca3d87f7736d3b1c56ba