Updated mediawiki/extensions
Project: mediawiki/extensions/Wikibase  b976bfe1429b5ffac8896c57b4c90581dca2a9c2

(bug 46383) correct constructor fields for prototypes not using wb.utilities.inherit

Since the object literal was used for those constructors prototypes, the original prototype's
"constructor" field has not been there. Now we extend the original prototype (which is also
just a plain object with the "constructor" field set) instead of overwriting it.
Also did some renaming and general cleanup around the constructors.

Change-Id: Ied01e553d16dd0b161fa97ea25d33d9f4efd0447