Change config format to use full category page names

* Include prefix (Category: or localized equivalent)
* Sanity check category names at runtime

This is because we're now using category names imported from a Wikidata
entity.

Change-Id: I51860b76f82b8760bd30630bcf76a3b17e9a3b56
(cherry picked from commit 31c0cfbb2791bbf9350c88406e33ef2dd8c432db)