Update FreeImage to latest CVS build
Redesign JPEG-2000 dialog to match JPEG one

The JPEG-2000 dialog will serve as the export dialog for a number of
other formats, so I wanted to get it cleaned up.  Code-wise it's very
similar to the JPEG one, but with much fewer options.
WebP export support with live previews!

I doubt that WebP will ever be relevant as a mainstream format, but
since FreeImage added support for it in 3.16, there's no reason I
shouldn't too.