Sanitize non-ASCII characters out of memorial file names. [WIP]

Fixes #2845. I think.

I don't actually have a way to test this as I have no idea how to type Chinese characters into Cataclysm. It's a simple enough patch, and it SHOULD work, but I'd appreciate one of the international users confirming that it does what it's supposed to, at which point I'll take the [WIP] tag off.