Hg 384

DO NOT merge just yet

This has to be deployed first:
https://github.com/Wikia/app/pull/5569

then this can be deployed

and at the end:
https://github.com/Wikia/wikia-vcl/pull/325

Should be simple and easy :)

Hypothetically this may be wrong in the case when you access custom domain through `wikia.com` sub-domain . Canonical URL will then wrongly point to the sub-domain URL, which may lead to duplicated content.