Maintain extension-list-wikidata with Wikidata build (beta only now)

We are moving towards using a "build" of Wikibase + dependencies.

(submodules temporarily now on beta and we will directly commit
all our libraries here in the future for deployment)

See https://git.wikimedia.org/tree/mediawiki%2Fextensions%2FWikidata

In maintaining our extension list here, we can keep things in sync
and not break beta when something gets moved.

Change-Id: I7d61433ab7e97efc4ad9dfa90de43c5ca9f5771e