Replace Wikipedia for Schools with Kiwix

After a conversation with Julian Hardy of the RACHEL project, I am convinced that we should switch to Kiwix for the following reasons:

According to Julian, WfS is no longer maintained. There will be no more updates.
Kiwix uses a compressed format in which Wikipedia is 2+ gigs, vs 6+ gigs for WfS.
As shown on their web page. Kiwix includes the option to have a bunch of other wiki* resources.

tunapanda / provision