Updated mediawiki/extensions
Project: mediawiki/extensions/Wikibase  61d56285f0f9563c315144ac10be3a796dcb077c

(Bug 47288) Use EntityUsageIndex on the client.

This also overhauls the way the SiteLinkTable is used, for
consistency.

Change-Id: Ide20d01f2c38047e6a640f1b3910df3b3cc9e69a