Introduce wikibase.experts.__namespace

Change-Id: I8e6437c3579eefebe712d3f6b035dffb50ae339a
Rename wikibase.experts.js

Change-Id: I9f3c51c8b55691a9770f9895593b1e533623c0c9
Merge "Introduce wikibase.experts.__namespace"
Merge "Rename wikibase.experts.js"