Allow the same filtering on Special:NewFiles as on Special:NewPages.
I was originally thinking that we could do this by reusing a lot of Special:NewPages code, but I looked into it and that won't actually work. Pretty much everything is different on the inside (other than generating a list of things). We have different needs for the rendering, and we have different queries (we're querying logs rather than page revisions, to start with). So I'll just have to reimplement the bits that make sense.