Add audio/x-opus+ogg mime-type

https://bugs.freedesktop.org/show_bug.cgi?id=63106
Add image/x-webp mime-type

Magic information from:
https://developers.google.com/speed/webp/docs/riff_container#webp-file-header

https://bugs.freedesktop.org/show_bug.cgi?id=41155