Move mediawiki install to using the debian package

[frankduncan]

Talked about here:

https://chat.opentechstrategies.com/#narrow/stream/45-Lever-for.20Change/topic/Servers/near/82799

But what it boils down to is that instead of installing N different mediawiki instances, one for each competition, we should use the main mediawiki debian package. This will allow us to ensure that all wikis get updated at the same time, and that they stay up to date via the normal mediawiki updates.

To implement it, there will need to be fancy symlinked things by which the directory knows which LocalSettings to pull in in order to display the correct wiki with the correct permissions. However, all extensions will be available to all wikis, so those will similarly get updates in general. This will simplify the install, as the extensions can be moved out into their own ansible files, as opposed to being looped in and duplicated on the main ones.

Then, when ansible installing a new competition, all you have to do is enable them by updating the localsettings file correctly.

There is a small issue that when updating major versions via debian, you will have to run update.php manually for all installed competitions, so code should be written to help ease that process. That should be relatively rare.