Mediawiki importer 1.13.1, 1.13.2, 1.13.3, 1.13.4 and 1.13.5 released

With a lot of testing and debugging help, the MediaWiki parser and importer got a bunch of bugfixes and bulletproofing.

See https://extensions.xwiki.org/xwiki/bin/view/Extension/MediaWiki/#H1.13.5 for more details.