Replace Wikipedia API calls by an offline static snapshot

[kelson42]

To be able to propose an offline version Cheminfo, we need to replace Wikipedia API calls by "local" calls. That means having a local copy of the Wikipedia articles.

This might be done with the help of mwoffliner:
https://sourceforge.net/p/kiwix/other/ci/master/tree/mwoffliner/

I see two ways of doing it:
1 - Implementing this as an option
2 - Implementing it as a part of the standard "dumping" procedure

PS:One advantage of having an offline snapshot of the Wikipedia articles is that it really allows to tune the Wikipedia article content.