Rework all WikiUtils calls to use JSON instead of XML

[CaptainSpam]

I'm pretty sure JSON either wasn't an option when I originally wrote those, or there was some reason I picked XML instead and it's just stuck around by momentum. This really ought to change; it's a lot easier to debug JSON output, and I don't really need whatever XML has to offer in this respect.

[CaptainSpam]

Update: Everything should be using JSON now, and all looks right as per the MediaWiki API docs, but neither the Geohashing wiki nor my private test wiki are cooperating with my code at the moment. Still working on it.