DWU days

This is an unusual, and likely temporary, category that's necessitated by the use of days of the year by the Game of Rassilon. Without this category, it'd be a lot harder to maintain the "vanilla versions" of the date pages, like 1 June.

We normally do not allow category names which directly include "DWU", "In-universe", or the like, and the existence of this category should not be taken as a precedent for creating more such categories.