Implement the file navigation as a Kino Control

[w0rd-driven]

I was wondering if it makes sense to pull either the full filesystem or just the file selection components to their own package to bundle into other smart cells. I could see the file upload concepts use something like that to have a more unified experience. I've also been itching to have something that synchronizes modules in notebooks to files as a companion to running along with applications.

I haven't dug deep enough to know if there are architecture hurdles that make this impossible or extremely difficult and not worth tackling.

[josevalim]

Livebook and Kino (the runtime part) are actually fairly isolated with a thin communication layer. We could implement this, but it would require a bit more coupling between the parts, which is something to consider overall.