[mod] settings.yml: enable engines from Wikimedia Foundation

The Wikimedia wikis [1] engines provide good answers and have short response
times --> no reason to disable these enhgines by default.  BTW: this patch adds
a (sub-) category ``wikimedia`` for the engines [1].

[1] https://meta.wikimedia.org/wiki/Wikimedia_wikis



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>