vivaldi-ffmpeg-codecs: init at 59.0.3071.104

Due to licensing costs, Vivaldi bundles a version of ffmpeg compiled
without support for the common H.264 codec. However, it is possible to
supply a custom libffmpeg.so with additional codecs. This derivation
uses the Chromium source to compile a compatible libffmpeg.so.

This approach is recommended by a Vivaldi developer, see
https://gist.github.com/ruario/bec42d156d30affef655