To get rid of the warning box "This extension stores its code inside a wiki page. Please be aware..." I will try to move the code to the MediaWiki code repository. To avoid doubling work, I will wait until this repository has moved from SVN to GIT.
Topic on Extension talk:GeoGebra
According to this topic on Wikitech mailing list, and Git/Conversion/status, MediaWiki core and WMF-deployed extensions were migrated to Git.
You may want to take a loot at Git/New repositories or try to contact someone on MediaWiki IRC channel.
I already had a look at Git/New repositories. Today I chatted on IRC channel. Your link to IRC Help page was very helpful, but I read it after connecting to IRC. Now I know to use /quit for quitting ;-) (I hope it was not too impolite just to leave the IRC by exiting the browser.) ^demon told me to read his mail about moving to GIT on wikitech-l, so I subscribed to the list. But I cannot find any postings of ^demon. Maybe he uses another nickname on wikitech-l? I also posted my username and email address at IRC #mediawiki. This should be enough to send me access data. Please give me a hint what I should try next.
User:^demon is Chad (I didn't know that either - until now) and you'll find some emails from him in the archives. Maybe he was referring to the same thread I suggested above?