Wikidata deployment

Deployment notes

 * purge the parser cache by bumping $wgCacheEpoch
 * make sure wikidata-shortcopyright message is handled properly

Changes

 * data type in json / api output
 * table of contents
 * sorting
 * ranks

Other

 * improvements to the link item widget in the client
 * using parser cache now
 * improvements to page loading in backend

Bug fixes

 * diff=0 works - 49434