Uploading updated and improved version of the MpDisqus extension

The MpDisqus extension was only available through mediawiki.org
I downloaded the code, updated and improved it, and I'm now
uploading the extension for the first time to Gerrit, and with
a new name (the previous one was based on the name of the first
author, plus it didn't suggest what it does).

Change-Id: Ibe700bf9fef099ab852b54dc100dda6903c2daf1