Fetch some config from mediawiki API

This should be a leap into the fray when it comes to language support.

* Namespaces should all be fetched per-wiki
* Namespace aliases should work now
* Magic word aliases are also fetched
* As are special page aliases
* And in future, we can support i18n'd extension tags.
* We can also use this same config to support i18n link(trail|prefice)s.

Change-Id: I0e2480373595897fdc880359b69793dc688fd509