Investigate how to handle 3rd party wikis without TextExtracts or PageImages

[mooeypoo]

Egh,

• https://www.mediawiki.org/wiki/Extension:PageImages
• https://www.mediawiki.org/wiki/Extension:TextExtracts

Both of those are mandatory for wikilookup and yet they're not bundled in MediaWiki tarballs, which means that a private wiki may well not have them.

Need to try and figure out what to do with this; either document this properly (encourage people to install these two) or see if there's a way to use the raw API to get what we need.