Better image support about kino

[cocoa-xu]

Hi @josevalim, I'd like to add support for camera input if currently no one is working on it. :)

[josevalim]

Yes, please go ahead. Let’s start with camera image first, so there is an explicit click button to take a picture?

[cocoa-xu]

Yeah, I'm thinking something like this:

And, of course, we can probably also make it optional here, something like Kino.Input.image("Image", camera: false).

Linked PR: livebook-dev/livebook#1595