Use mediawiki install from debian instead of deploying ourselves
Created by: frankduncan
Currently the mediawiki tar is downloaded for each competition. Then it's updated and configured. That means that when mediawiki updates come, we have to update and redeploy all previous competitions fully, which is unlikely to be done. It also doesn't work well with the way we like to keep our systems up to date.
The catch is that MediaWiki is really set up to have on wiki per machine. That means that there's one LocalSettings file for the machine, and one set of extensions. So some magic needs to happen so that the LocalSettings is different for different competitions based on paths.
Likely there will be one installation, with all the extensions that all competitions need in the extensions folder. But then each local settings that's loaded via symlinking magic will load the extensions pertinent to that competition.
There's an issue that running maintenance scripts from the global directory will fail, so on debian updates, if update.php is run, that will fail. Even if we make it so it doesn't fail, it will still need to be re-run for all installed competitions.