Clone MediaWiki core, skins and extensions

Summary:
Clone from Wikimedia Gerrit setup the repositories and run composer.

Ref T845.

Test Plan: Deploy on Ysul, check if /srv/mediawiki looks good

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T845

Differential Revision: https://devcentral.nasqueron.org/D1437