Updated mediawiki/extensions
Project: mediawiki/extensions/Wikibase  e0c68bd84a5c6598d547f7e21b4c95bd804a7266

Work on data value tables access in the SQLStore

* Moved all schema knowledge into a new Schema class
* Split of declarative part of DataValueHandler into DataValueTable which is now composited into the former
* Created DataValueHandlers to hold the registration of default DataValueHandler objects
* Added some prototypical code to the Updater class

Change-Id: Idd882b70fb96cc68e3261849756e19698b05f84b