Updated mediawiki/extensions
Project: mediawiki/extensions/MobileFrontend  586ac94b8d90ad7665a8b9eb8f5706892946d745

Remove unused images

Add a script for detecting unused images and move mw.png out of
stylesheets dir, it's not used in CSS.

Change-Id: If8a379d7dbb5ebe43ebf1e218143b3e8819b9ff7