Make wbclient.linkItem experimental for now + non-JS fallback

We for now only show a link to Special:CreateItem on the repo
in non-experimental set ups. That link will also stay for users
without JS.

Change-Id: If935aa23e819bdeccdb8d37ea28268c2571445dd
Merge "Make wbclient.linkItem experimental for now + non-JS fallback"