Wikidata deployment

Rationale
See Wikidata for more information about the Wikidata project generally.

Deployment

 * See the deployment plan on Meta.

Blockers

 * See blockers on this tracking bug: ✅

Core changes
Wikidata patches awaiting review:
 * Gerrit 14295 - Adding sites handling ✅
 * Currently awaiting merge or comments ✅
 * - Merging the Wikidata branch (ContentHandler) ✅

New extensions
The whole Wikibase code (5 extensions: repo, client and shared code in lib and diff) needs a review (and has partially gotten it already):
 * Repo ✅
 * Lib ✅
 * Client ✅
 * Diff ✅
 * DataValues ✅
 * We are also using the Universal Language Selector ✅

Communications
See Wikidata on meta for all channels (IRC, mailing lists, wiki pages, meet ups, etc.)

Miscellaneous

 * Wikidata/2005 proposal - original 2005 proposal for Wikidata