Automatically install latest ffmpeg version in script

[mayeaux]

I do this already with videodownloader, no reason to not just ship the latest version of ffmpeg with NodeTube, saves people having to deal with a dependency as well.

[mayeaux]

https://github.com/eugeneware/ffmpeg-static
https://www.npmjs.com/package/ffmpeg-static

var pathToFfmpeg = require('ffmpeg-static');
console.log(pathToFfmpeg);

If this is used instead of the machine's native installation it will reduce errors and ffmpeg can be removed as a dependency.